>kanto
Could use some better story, post-game is lame, Sevii Isles have potential that is ultimately a chore
>Johto
Level curve memes are real. After Morty the game becomes a slog. Story is non-existent. Variety of cool areas that lack any lasting impact despite being cool.
>Hoenn
Strong for so long...then you hit the sea. It's great thematically and in theory, but jesus. The "fast water" routes needed either more to them, or the whole southern strip needed to be reworked. An archipelago would have better suited the purpose - lets you have non-water pokemon distributed more evenly, and could have dipped toes into tropical-themed pokemon at a time when that was very popular in games. Moderate hm bloat, evil teams could have used more presence.
>Sinnoh
Mon distribution / dex size, cross-gen evos were ALMOST a smart decision...except half of them are locked behind an item+trade, making them a whole lot more trouble than they are worth. Just needed more mons, I won't touch the fire type meme as it's just a symptom of the actual problem. Also HM bloat, and pretty much the instant you beat gym 5 (regardless of game), then game starts to peter out hard. I have no doubt they ran out of time with these games, and they are deeply flawed while being very interesting.
>Unova
If I have to read one more shitty dialogue box, I swear to God. Routes were interesting, but dragged down by a preoccupation with there needing to be SOMEONE or SOMETHING on every route. Crown jewel was clearly meant to be the big city with the bug gym, but it just felt excessive and overwhelming, making it a failure (worse yet, it's empty). Clearly a strong effort to develop a deeper pokedex, but I'm willing to bet a number of sinnoh-mons that didn't make the timing cut wound up here as slush. Hurt heavily by the echoes of the kanto dex, despite decently designed mons. The games with the most untapped potential.