Say what you want about Gen 2, at least they didn't introduce a Poke-Ice-Cream, unlike a certain generation did >.>
Generation 2 I could easily consider one of the more successful generations, due to a number of factors:
-Tied in perfectly with a former generation
-Was introduced while Pokemon was still "Fresh"
-Most fans who refuse to acknowledge future generations of Pokemon and stay faithful to the original 151 will still accept Gen 2
-Introduced the concept of minor Legendary pokemon having their own story (Beasts)
-Kept the simple gameplay
-Introduced 2 new types
-Didn't go overboard with new Pokemon
Honestly, that list is probably missing a few points, I just can't figure them out.