>>368180801. Battle animations introduce a camera that moves all over the place which slows the pace of the game down (like people like to complain about Sinnoh games) and disorients the player, on top of shoddy sprite-work that is overly pixelated and generally very conservative in Pokemon posing, compared to what previous iterations could accomplish because of using still images.
2. Bad game balance. Worst is Serperior, the most useless starter in BW due to terrible movepool and a stat distribution it couldn't take advantage of because of its poor defensive typing. Why? To balance for a massive buff delayed for years in the form of its Hidden Ability, Contrary, which you as a player didn't have access to at all. Ferrothorn, on the other hand, went on to find itself on nearly every competitive OU team for the whole generation.
3. The story wants to take the angle "Is Pokemon training bad?", and goes the length to force the player to have this strange relationship with N, who is supposed to be a stalwart opponent of keeping Pokemon, but instead eventually comes to see things your way after all; the real bad guy just wants to take over the world. So you have to deal with this guy constantly getting in your face throughout the story, and in fact, the credits roll just as he's being given this grand exit entirely devoted to how sad it's supposed to be that the player will never see him in the game again. You can't even fight the real champion until said credits roll.
4. Poor Pokemon designs that are almost all blatant rehashes of Kanto Pokemon. This is neither a lie nor an exaggeration. This is a demonstrable fact. They are highly simplified in terms of shape, as well as the inspirations for their design---the execution involves far less fusing of concepts that made most Kanto Pokemon more than just real life animals made into cartoons.
5. Sound design is all over the place. E4 theme? Yay. Rival theme? Ew. Champ? Disappointing. Credits? Jarring.
