The movie version of The Flash is going to be adapting the Flashpoint storyline, which helped to launch the New 52 back in 2011. As a movie, this works for Warner Bros. on multiple levels: it’s a well-known storyline to draw in fans and gives a story reason to reboot parts of the DC Extended Universe that haven’t been well received. The trouble in adapting such a big and well-known storyline is that there are always a number of ways that it can go wrong. Luckily, there’s an example they can learn from.
When Season 2 of The Flash ended with Barry Allen traveling back in time to prevent his mother’s murder, fans were excited to see the Arrowverse version of the Flashpoint story. It was not well received, and looking at why that was can help The Flash movie deliver a version of Flashpoint that fans will find more satisfying.
Explore the 'bad' alternate timeline
The Flash spent an episode in the alternate timeline of Flashpoint, and it really wasn’t all that bad of a world. Sure, most of the things that were familiar to Barry were off - Joe was a drunk, Caitlin and Cisco weren’t at Star Labs - but they weren’t that bad all things considered. Doing the comic story, where Barry Allen finds himself in an alternate world torn apart by a war between Atlantis and the Amazons, was probably never in the cards, but what happened in the show just seemed so small.
The movie can go bigger, as well as spend a lot more time in the world of Flashpoint. They’ll have the extra work of building a world for The Flash, as we don’t really have much of Barry Allen’s life from his appearance in Justice League and brief cameos in Suicide Squad and Batman v. Superman: Dawn of Justice, but that’s much more doable in the runtime of a movie than a single episode of television.
Don’t be afraid to make changes
By the end of the “Flashpoint” episode, things are basically back to normal in the world of The Flash. Caitlin becoming a metahuman is a big change, but nothing else sticks or matters for long. The other biggest change actually comes over on Arrow, where instead of a daughter, John Diggle and Lyla Michaels had a son. As big, world-changing events go, that’s really not a big deal.
The movie has a lot more freedom to change just about anything they want about the DC movie universe. Sure, go ahead and keep Wonder Woman, Aquaman and Shazam - people seem to like them - but the earlier stuff, including Batman and Superman? Go ahead and blow that all up. When this Barry Allen comes back to (almost) the original reality, you can change anything, and given the mixed reception to the movies so far, it’s recommended to change a good deal.
Have fun with it
After coming back to the present with his mother dead again, Grant Gustin’s Barry Allen is a pretty sad guy. Previously happy and high energy, he spends most of the season being dour, which the fans really didn’t like. Barry spends much of the episode alienating his friends, constantly mentioning his Flashpoint gaffe whenever they're down as if he's trying to one-up everyone.
Ezra Miller’s Barry Allen is similarly high energy, in contrast to the universe he’s in. As much as he’s dealing with heavy things -- he creates a dystopia by trying to save his mother from being murdered - he seems like a fun guy. Let him have fun, even as he’s dealing with such a heavy storyline, and come out of it with a positive outlook, even if the heaviness of what happened has changed him.
Make it a story
The biggest failing of The Flash’s version of Flashpoint is that it didn’t really tell a clear story. Barry changes time and things are mostly okay but bad in a couple of places, so he feels guilty and goes back in time again to let his mother die this time. It tries to explain why he would do this, but never really sells this big of a character change in such a short amount of screen time.
By providing a more interesting alternate timeline, the movie can make this journey clearer. The backstory of his father being wrongly imprisoned for his mother’s death was in Justice League, so we can assume the movie will start with a number of the same beats. This story should be more about how selfish he is for changing the world to meet his whims and exploring the potential horrible consequences of changing the timeline. Done well, this can make a compelling story about how Barry changes his mind and realizes how selfish he is to put his own wants above the rest of the world.
The best way to learn is from someone else’s mistakes, and The Flash movie has a great opportunity to do so. By looking at where The Flash TV series dropped the ball with “Flashpoint," they can see how to better adapt the story when taking their shot at it.