>>47785528It lacks polish.
What you would expect for being the first in the series. Great at the time and it still holds up (I think), but it has issues. Special is one stat, environments are a bit flat, buggy, etc.
>>47785542Bad level curve.
It's totally beating a dead horse at this point, but after the Johto E4 every trainer you face is at a much lower level until Red, who is likely around 15-20 levels stronger than your team. The Kanto half of the game just feels kind of blah compared to the Johto half because of it.
>>47785564The stat overhaul.
Stuff like Natures and IVs isn't exclusive to Gen 3, but considering the phys/spec split didn't exist at this point stats felt a bit wonky. That's not to say that the phys/spec split is necessary (I think GSC is fine without it), but when you have a mon that's already kind of flawed like a Dark-type physical attacker and add to it that NOW it can also have a Nature that makes it even weaker, it just feels kind of frustrating.
>>47785584Slow.
Inflated HM use, the health bar (which is also kind of beating a dead horse but in a game that revolves around battles it's pretty annoying), etc. If they just made the games feel like less of a slog I'd be more inclined to replay them more often.
>>47785596Availability issues.
Gen 5, BW specifically, made it so that you pretty much only have access to the new mons for that region. Which I'm totally fine with, but a lot of them are a pain to actually obtain or use. Some are harder to find depending on the season, some have high level requirements to evolve, a lot of them are trade evolutions, etc.
>>47785621Too easy.
This is kind of subjective, and every game in the series is arguably easy, but you don't even have to try in these games. Along with the addition of the full-team Exp.Share, all of the trainers/gym leaders/villains/etc. are complete pushovers. It feels like you're not accomplishing anything as you progress through the game because of how little challenge there is.