>>29515792Sales don't really indicate how good a game is, just how much it's marketed. BW/B2W2 had the misfortune of being released close to the end of a console's life and aren't marketed as heavily as XYORASSM.
They're still very good games if you're looking for a fresh experience. B2W2 has an excellent postgame, though it's a sequel to BW. BW are polarizing because you only encounter gen 5 mons in Unova (similar to how you only encounter Kanto mons in Gen I and FrLg). There's also a heavier focus on the story which some people like and others don't.