They all have their high points, and I love them all (except B/W2 and that's only because I haven't played it yet), so the worst has to go to Gen 1, if only because they're not as technically advanced as the later series. Even though to a lot of people, myself included, that simplicity is part of its charm.
The main villains were awful, the pokemon were bland
dude you just described gen 2
BAWW GIOVANNI BAWWWWWWWW and lol most gen 2 pokes
Yeah, that's true, but I personally loved the Pokemon of Gen 2. Phanphy and Totodile are my buds. But Gen 2 also brought in new features like Time/Day/Night and the Bug Catching Competition that was always fun IMO.
Plus, the fact that you could revisit Kanto and challenge them + Red and Blue was just awesome in itself. Overall Gen 2 was better than Gen 4 IMO. Only good thing I can say about gen 4 is that the real Special/Attack split that actually made some of the useless pokemon useful.