The original series of Pokémon holds a special place in the hearts of many, being their first introduction to the world filled with incredible creatures of designs both beautiful and questionable. Following Ash in a time before fans realized he was always going to be 10 - even though he has had a canonical 11th birthday - there's something about his first adventures that really stand out.
Despite what nostalgia tells us, particularly in regards to the X & Y or Journeys anime, things do, in fact, get better over time. That's not to say the original series isn't bad by any means, but it definitely feels dated compared to today's standards, which means not every season stands up to the test of time.
5 Adventures In The Orange Islands
This short filler season followed Ash in the wake of his embarrassing defeat to Richie during the Kanto League, as he takes on the Orange League for a chance at redemption. There are many good aspects to this series, from Ash making full use of the Pokémon he has caught in his adventures as well as adding two new Pokémon to his roster in Snorlax and Lapras. Arguably the best part of the Orange Islands season is when, after suffering a humiliating defeat at the hands of a Poliwrath, Ash's Charizard finally starts to respect his trainer and listen to him in battle. This was a huge turning point for both characters, as Ash keeps this trend of treating his Pokémon with love and respect throughout the rest of the series and doesn't have issues with disobedient Pokémon again. As for Charizard, this singular episode cementing him in fandom as one of Ash's strongest Pokémon ever, possibly even his strongest.
As for what the series lacks, aside from the very short length, is that the battles themselves aren't very entertaining. The Orange Island badges are won through trials not unlike the island trials in Alola, though, because there are only four badges, they're over before they ever really begin. The battle against Drake, the champion, isn't bad but it has aged along with other battles from earlier seasons of Pokémon to be far less interesting. It also has the unfortunate ending of Ash's Pikachu winning by aiming for the horn on a Dragonite, a Pokémon that has no resistances to Electric-type attacks.
4 The Johto Journeys
The Johto region is often overlooked in terms of the Pokémon Ash catches, as he caught very few compared to the ones in Kanto and the Orange Islands, but the ones he did catch have stood the test of time and many made a return in the Lily of the Valley Conference in Sinnoh as powerful team choices. While he didn't catch that many Pokémon, all of the ones he did catch were in The Johto Journeys, giving the entire Johto saga enough time to flesh out each new addition as their own character.
The cons of The Johto Journeys season is that it is far too slow-paced compared to any other season of Pokémon. By the end of its 42 episode run, Ash had barely defeated Bugsy, the second gym leader of Johto, with a huge chunk between gyms being unnecessary filler episodes. While some of these episodes were also dedicated to his Kanto starter Pokémon moving up in the world, with Squirtle returning to the Squirtle Squad and Charizard being left for some training in Charicific Valley, there was far too much time spent aimlessly wandering around towns for this season to be ranked among the best.
3 Indigo League
The very first season of the entire Pokémon series, and by far the longest. Coming in at a whopping 82 episodes, Ash's adventures in Kanto, while actually shorter than his adventures in other regions, are action-packed and full of fan-favorite episodes. From classic Charizard episodes like Attack of the Prehistoric Pokémon and Volcanic Panic, to the more heart-wrenching stories in Bye Bye Butterfree and Pikachu's Goodbye, there's something in this season for everyone. The Indigo League season was also the beginning for many long-running characters in the series, such as Brock, Misty, Gary Oak, and Delia's Mr. Mime, who has since made a return onto Ash's current team in Journeys.
While this season is a little bogged down by Ash's stupidity and beginner nature as a trainer, it is helped by the fact that it is the very first season, and as such, the audience were often learning new things about the world of Pokémon at the same time Ash was. There were also some questionable story and animation choices in the first season, which led to a handful of episodes being banned and Pokémon like Jynx and Porygon almost never appearing in the following seasons as a result.
2 Johto League Champions
Despite the name, the Johto League Champions season wasn't the one of Ash competing in the Johto League, and was actually the follow up to The Johto Journeys. This season follows his adventures from his battle with Whitney, the infamous Miltank trainer, to the Fighting-type gym leader Chuck in the final episode. A little more fast-paced than the preceding season, Johto League Champions follows on from Ash's growth after his battle with Falkner in Johto Journeys, where he realizes that he can't simply brute force his way through battles and needs to strategize to win.
This season of Pokémon also marked a shock twist at the time, with Ash's Chikorita evolving into Bayleaf after a battle with Team Rocket, an event that would happen again with his Cyndaquil while training for the Sinnoh League. While Ash would go on to actually evolve many more of his starter Pokémon in the following seasons, it seemed for a while like he wouldn't with the exception of Charizard.
1 Master Quest
The final season of the original series was probably the most eventful, as not only did Ash finally compete in the Johto League, but he also finally defeated Gary Oak in a battle, something he hadn't had the chance to do since the series began. Master Quest also marked the departure of Bulbasaur, one of Ash's best Pokémon at the time, as he needed to return to Professor Oak's lab to act as a mediator between Gary and Ash's Pokémon, who were causing problems for the professor. To fill the void Bulbasaur left, Ash received a Pokémon egg which quickly hatched into a Phanphy who, although it would be used quite often, wouldn't shine until the Advanced series.
While the Kanto League battles were quite fun to watch, particularly Ash's sweeping victories using a Krabby he had never battled with before and his Muk making mincemeat of a ridiculously powerful Bellsprout, they don't compare to the battles Ash had in Master Quest. The highlights of this season easily go to his victory over Gary Oak using his Charizard against Gary's starter, Blastoise, as well as his loss to Harrison and his Blaziken which triggers the desire to travel to Hoenn.