Orange Islands needs more love, and the Johto seasons were the funniest Pokémon's ever been (as well as having one of my favorite Ash moments in admitting to Charizard he's not experienced enough to raise him, it's controversial but Ash made the right call imo), but they were so damn slow getting to each gym, and unfortunately at the Johto League, Ash relied more on his original teammates instead of his Johto team. Advanced Generation at least went out of its way to improve upon what it learned from Johto, but it still sadly underutilized Team Magma and Aqua, and the Groudon and Kyogre battle was overhyped and didn't live up to it. Max, although not a bad idea to have a sibling dynamic in the team, honestly bogged the whole series down despite their best efforts to try and give him a character. I don't even know if Bonnie is better or worse, still struggling to get through D&P, of which I think Brock coming back wasn't really a good move since even in Hoenn it felt like he overstayed his welcome. Battle Frontier I think wasn't a bad season, but the dub-change midway through hurt its reputation.
Indigo League is still a fun watch, but there's a reason the "pity badges" are always noted as a negative, because half of them were interrupted matches of which he was either winning, or he was losing, but he did something heroic to impress the gym leader to give him the badge anyway (and he would actually protest this). Sabrina's gym is an egregious one, too, though he didn't speak out about that one. This is why after the Orange Islands, you actually got to watch his gym matches from beginning to end and sometimes, he actually lost and had to have a rematch where he actually showed he could learn from his mistakes and come up with strategies to overcome them. So the battles have improved since the first season, and that's a good thing.
I will admit the redesigns for Joy and Jenny in later series ruined their waifu statuses, though. Honestly am not a fan of their looks past fourth gen.