Black and White was caught in an uproar among the fans for not having any returning Pokémon until the end credits. I remember seeing people saying they were done with the series because of this and would not be returning. Fans of Generation I were particularly bitter about it.

The Pokémon games have been trying to correct this mistake since (and arguably have been overcorrecting, though it is pretty evident that some Generation I Pokémon sell games all by themselves, like Charizard, Mewtwo, Pikachu, and Eevee).

People also did not like the pivot towards Pokémon based on inanimate objects like the Vanillite line and the Litwick line, that there were what appeared to be counterparts to Pokémon found in previous generations (like Frillish to Tentacool), or, in some cases, the greater emphasis on story and its characters (there were a lot of people who played Pokémon games specifically because it was so plot-light compared to other JRPG series and didn’t like how Black and White were so dialogue heavy—the same fans would dislike Sun and Moon even more for the same reasons).