While I like Team Plasma, Gen 5 was my least favourite. Nothing (in the environment at least) really wowed me in either BW or BW2 The big city in the middle with the pseudo 3-D was nice and all, but in the end, there wasn't really much there and it kind of felt like an unfinished game compared to HG/SS. I grew up playing Gen 2, so I'm most fond of that one because of it's massive post-game and the Johto region is just full of culture unique to the game which you don't really find in other games. Gen 3 would be my next best favourite because of the exploration in the game, Dive was such an awesome mechanic and the story behind it is pretty nice too. Pokemon Blue was my first videogame like ever, I still remember the time I got it with my Gameboy Pocket. Gen 4 had a meh story and a really meh region which didn't really do anything for me, but the Physical/Special split was a big advancement in competiitive battling (Gyarados yay), and so, 4 would be my second least favourite.