CAUTION: Multiple spoilers for "Flash," "Arrow," "Supergirl" and "Legends of Tomorrow" below!

As the CW Network has launched into another round of superhero shows, the roster has grown increasingly packed each year. "Supergirl" recently joined the ranks of "Arrow," "Flash" and "Legends of Tomorrow," ready for everything that comes with such an honor, including taking part in crossovers. Much like their comic book counterparts, these CW shows share the same universe and thereby have the luxury of heroes making guest appearances in different series.

RELATED: 15 Reasons To Start Watching "DC's Legends Of Tomorrow" Again

While it may be fun to see Cisco hamming it up with Ray Palmer, or Constantine imparting some advice to Oliver, these guest episodes are generally over-hyped, rushed or otherwise lackluster. As much as we love these crossover events, they're very quickly turning into the Achilles' heel of the CW hero universe for a number of reasons.

15 Not All Episodes Are Relevant

The biggest grievance fans had with the most recent CW crossover, "Invasion!", is when heroes Barry Allen and Cisco Ramon made a guest appearance in "Supergirl" for a handful of minutes at the tail end of the show. This rendered the inclusion of the "Supergirl" episode almost completely irrelevant to the meat of the big story. Fans were understandably irritated, citing a bait-and-switch tactic for such a bare bones appearance by their favorite "Flash" characters in the newer show. To make matters worse, the entire scene was repeated on "Flash" the very next night, so viewers could have skipped "Supergirl" entirely.

While this may be a one-off in this type of appearance, it stands to reason that it may end up being a more prevalent practice in upcoming episodes. Since the CW now has four superhero-themed shows (with who knows how many more in the future), having longstanding plots span over multiple episodes will likely prove difficult. Not only for the production, but also to keep the audience engaged across several different shows they may not necessarily all watch.

14 Everything Happens Too Quickly To Fit It All In

This is something that is felt with practically every crossover episode in these series. A great example would be the Constantine appearance in "Arrow," which managed to somehow have the master of the dark arts properly resurrect Sara in the present day, while also unearthing long-lost spiritual artifacts in the past, all within about 40 minutes of runtime. Even more so with "Invasion!" being across three full episodes, the aliens went from an all-encompassing threat to neutralized in what seemed like no-time for the superheroes.

Given that most of the characters are essentially "borrowed" from other shows, their time is incredibly limited per episode. This makes their appearances all the more fleeting, as they usually serve to quickly eliminate a big bad of some sort and hustle back to their respective cities. The lack of staying power for these characters is a detriment to the crossovers because they can't commit to story lines that require more than an episode worth of a character's time.

13 It's a Terrible Way of Introducing Characters to Each Other

With all the characters clashing from different shows, introductions are usually in order in some way, shape or form but always end up heavy-handed. Hawkman suffered this particular issue in his debut "Arrow" episode called "Legends of Today." The hero literally flies in, rattles off his origin and link to Kendra (a.k.a. Chay-ara) and is immediately accepted into the fold within minutes. Supergirl got similar treatment in the more recent crossover episodes, as Barry simply tells the others that since they're fighting aliens, he brought one from another Earth. Kara, a being from an entirely different world that has powers beyond imagination, literally gets a sentence of exposition before she is absorbed into the ensemble.

Granted, many of these guest episodes start off with a dire situation that requires another hero to join the fray, and could arguably eschew the need for a proper introduction. The way it's handled in these crossovers, however, is just plain lazy. Having characters get acclimated to new people just as quickly as the audience has to is yet another problem these team-up episodes suffer.

12 They Don't Contribute Much to Their Respective Shows

For all the gusto each show tackles their crossovers with, most don't really have any lasting effects once they're all said and done. Oliver got a halfway-done tattoo of protection from John Constantine that didn't do much, Kara got a handheld portal opener (which might as well have just been called a writer's loophole) and Kendra sort of tapped into her powers, even though she continued to struggle with using them in "Legends." Whatever progress characters seem to make during these mash-ups seem to be undone or not matter much when applied to the bigger picture.

It's a bummer that lessons learned during the epic crossovers don't really go far into the plots of their respective shows once everyone goes home. Even though they interacted with other heroes to assist with apparently bigger and badder foes, the characters don't leave with much more than they came with. This just furthers the weakness of these episodes, as a lot of their story developments are practically moot after the fact.

11 Existing Villains Seem Entirely Clueless of What's Happening

You would think when main villains such as Reverse Flash or Damien Darhk are as obsessed with their respective hero nemeses as much as they are, that it wouldn't make sense for them to not notice when one of them leaves for a spell or teams up with another. The rogues however, don't seem terribly worried or even aware of these crossover events. When Ray Palmer briefly helps out Barry, Reverse Flash didn't seem even remotely bothered by his involvement with the hero. Even when Vixen goes toe-to-toe with Darhk himself, he never figures her into his current list of Team Arrow allies once the episode is done.

While some may argue that both the villains and heroes hardly keep a day planner with each other, it still stands to reason that a stalwart enemy would be ever aware of their nemesis' every move. During these crossovers the main villains themselves never appear to question where the hero might be, who these new people in town are or what chaos they can bring while the city's protector is away.

10 Tons of Plot Gets Bowled Over so Characters are On the Same Page

Each show has its own respective story line that runs differently from the others. This being in a shared universe however, makes for some difficult dialogue in order to have all the characters up to speed. Ray Palmer breaking the news to Barry about Captain Cold's fatal sacrifice had all the eloquence of an elephant crashing into a piano during "Invasion!" Similar issues arose when Barry had to explain "Flashpoint" (for the umpteenth time it seemed) to the "Legends" and "Arrow" crew, mashing together several episodes' worth of information into a few throwaway lines.

This is frustrating because it's almost as if no one owns a cell phone in this shared universe. Laurel's untimely demise seemed to make the rounds just fine, but the crossovers feel the need to have everything laid out for each character (and viewer) that might have missed out. While the intent is positive, it gets delivered in the form of clunky exposition that lacks any real emotional impact.

9 Each Show's Storylines Get Paused to Accommodate the Crossover

No matter how powerful a villain might be in their respective show, none are apparently strong enough to function in their evil machinations without the hero around. This was most egregiously applied to "Arrow" when Oliver took a pause from his incredibly complex ruse of fooling everyone into believing he had become a full-fledged member of the League of Assassins, in order to assist Barry in a quick punch-up with the Reverse Flash. To think that Ra's al Ghul wouldn't notice Oliver's absence (or at the very least question him when he got back) isn't just a leap of faith, it's a downright blind eye.

There appears to be an unwritten agreement that time will practically stand still when characters visit other shows, which only stymies the main plot. This ends up making the crossovers more of a filler episode for their respective heroes, instead of a truly dire situation needing a team up as it's meant to be.

8 They Often Fall Into the Cliché of Heroes Fighting Each Other

Both "Invasion!" and "Flash vs. Arrow" are the most guilty of this, as they both relied on paper-thin plots that pitted characters against each other. As a matter of fact, both of these episodes in question used mind control as a weak excuse for Barry to go berserk on Ollie or the entire team turned against Flash and Arrow. Other instances such as Constantine or Hawkman introduced the characters as volatile unknowns that initially start their relationships with the heroes as uneasy enemies.

Either way, it makes the new characters incapable of simply explaining themselves first, or being lazily mind-controlled in order to elicit a cheap fight to excite fans. What's more is that the fights themselves are generally lackluster, usually resolved after a few quick blows, hardly constituting as a proper punch-up to begin with! Whichever way it's spun, this particular trait of the CW crossovers is getting old very quickly.

7 Character Conflicts Get Resolved Too Quickly

Remember when Ray Palmer had an entire identity crisis because he lost his A.T.O.M. suit in feudal Japan to an evil overlord and had to have Steel destroy it? Remember when he struggled for several episodes in "Legends" to figure out what exactly he brought to the team since he was technically powerless? The great character arc and growth for Ray in such a time was patently bowled over in the recent "Invasion!" crossover, as the Atom synthesized a brand new suit in order toe fight the incoming aliens. All that second-guessing and shaken confidence? Gone at the drop of a hat or, more accurately, the drop of a crossover episode.

Unfortunately, these guest episodes don't tend to figure into the longstanding arcs or intricacies of character growth to the given story at hand. Even worse is when it tries to do so, only to ham-fist the delivery, as with Cisco very quickly getting over his several-episode-long grudge against Barry for creating "Flashpoint." It's great to get everyone fighting on the same side, but it comes at the cost of the crossovers painfully sacrificing great character growth in order to do so.

6 Many Characters Get Lost In the Background

The problem of having crossovers with so many characters is two-fold. The foremost being that there are so many characters in a given series that inevitably a lot of them are going to get lost in the shuffle. If "Legends of Tomorrow's" ensemble cast wasn't difficult enough to delve evenly between, the issue gets literally multiplied when forced to include folks like Ollie, Barry, and more. Some heroes like Jefferson got a smattering of lines in the recent crossover, or in the case of Artemis, weren't missed whatsoever by their fellow characters.

This has only gotten worse with the new additions to the CW shared hero universe. As each show gets more interesting with its own complex set of characters, the more mired in deflated appearances (or absentee ones altogether) the crossovers tend to get. Usually it's in the form of maybe Diggle sitting a meta-human fight out, or Wells scheming in the background, but it still struggles to include everyone adequately. Which conveniently leads to the second part of the character problem...

5 Characters Get Shoehorned Into Crossovers Simply to Make an Appearance

In trying to make sure everyone gets a fair share of screen time in a given crossover, some characters get unnecessarily added at the expense of the story. Team Arrow's incredibly irrelevant heist to snag a microchip from a random villain during "Invasion!" is a poignant example of this. Rene, Curtis and Rory put down a bad guy, acquire some tech and resolve their meta-human prejudice in an effort that is largely useless to the main story. Caitlin Snow was similarly wedged into "The Brave and the Bold" crossover, for nothing else other than being an apparent expert on the biochemistry of a lethal boomerang.

These kinds of appearances are frustrating because while they're definitely efforts to maintain each character's status on their respective show, they come off incredibly forced and awkward. It's difficult for the CW shows because they seem to utilize an all-or-nothing mentality when it comes to character inclusion, with no happy middle ground for supporting players.

4 The Villains Aren't Really Threatening

If heroes need to reach out for even more help outside of their city to take down a big bad, it would stand to reason that the rogue in question is pretty fearsome right? Problem is that out of Vandal Savage, Prism (actually Rainbow Raider), Captain Boomerang and, even more recently, the entire alien race called the Dominators, none of them come off as a particularly large threat in these respective TV events. Savage has a kooky plan to destroy everyone that gets easily erased by Barry, Boomerang gets put down by Ollie within minutes, and the Dominator's master plan of dropping a big bomb on Earth is foiled quickly with Firestorm's abilities.

For all their supposed villainy, with the exception of Savage, all of these rogues are quickly felled and never heard from again. Due to the nature of the crossover format, these bad guys have zero staying power and can only function in these short bursts for team ups. This ends up making the so-called terrifying villain not all that threatening since they only last an episode (or two) at best, versus the season-long rogues like Zoom, Ra's Al Ghul and otherwise.

3 They Can't Live Up to Their Own Hype

Whether it be an aforementioned cheap brawl under the influence of mind control or lackadaisical plot with characters all over the place, the crossovers simply can't live up to the fan expectations of such awesome team ups. Favorite heroes get overshadowed while others get touted too much, or vice versa. Most of the time, the heroes tend to get bogged down in exposition just trying to get up to speed with each other before actually getting in on any of the action.

As much ambition as the crossovers have, they never quite hit the mark when they finally debut. The promises of superheroes tussling with some of the mightiest foes around do get fulfilled, but in short sequences that are all too quickly wrapped up. Granted that no episode will ever appease all of the fans, but the CW crossovers struggle to integrate characters fluidly and leave the viewers with a somewhat disappointed viewing experience.

2 The Tone is Too Inconsistent

Juggling a story between different shows is difficult and it only gets more so with each new superhero show the CW kicks off. Only issue is, "Flash," "Arrow," "Legends of Tomorrow" and "Supergirl" have their own unique style, so blending an overarching plot between them is downright bumpy. Such an example is the relative seriousness of "Arrow" characters being turned around to suit the more bubbly nature of "Flash" and "Legends of Tomorrow." The quick-thinking Felicity and gun-toting badass John Diggle of "Arrow" were relegated to vomiting comic relief in the "Invasion!" crossover episodes; completely differing from their regular personalities in Oliver's show.

The same applies for other characters to the other shows. "Flash" folks tone down the metahuman diatribes to suit "Arrow's" more grounded themes, "Legends" cuts down on the sillier time travel sci-fi elements when guesting on "Flash" and so on. The entire web of these guidelines ends up leaving the viewer with an incredibly disjointed experience across every crossover episode they watch.

1 There's No Consequence to What Goes Down

When Barry managed to travel to another Earth and team up with Supergirl, he hardly had any mention of this newfound ability or comrade once he got back home (till the next crossover episode that is). Oliver and crew manage to actually incinerate Vandal Savage to ashes at the end of "Legends of Yesterday," only to have the rogue back and at 'em in "Legends of Tomorrow" with nary a misplaced beard hair. Aliens literally rained from the heavens and yet the inhabitants of Central and Star City seemed largely unperturbed by the whole affair.

The bigger and crazier the events in these crossovers get, the more you would expect the stories to have lasting power over each show. However, each event is so self-contained that regardless of what amazing feat a character pulls off, it's largely relegated to throwaway lines in follow up episodes. The lack of a fully invested crossover story with these team-ups is disappointing, given how much more depth it could add to this ever growing CW hero universe.

What do you think is the worst thing about the crossovers? Let us know in the comments!