Most of /vp/ agrees that Gen 5 is the best gen. The only people who disagree are a small group of Gen 2 fans.
BW is the first gen that captures the feeling of being brand new since the originals. Having no older Pokemon catchable until after the Elite 4 was one of the best things GameFreak has ever done. BW also executes a story very well. B2W2 put a spin on the "1.5 version" formula and tells a cool tale. Both games have great post-game challenges, especially B2W2.
The only spot where Gen 5 dropped the ball is legendaries. The genies, Meloetta, and Keldeo are pretty lame, but the cover legendaries are some of the best design and lore-wise.