I must disagree.
Pokémon Black 2/White 2 are more than just rehashes like Crystal, Emerald, Platinum, etc. were. They've got entirely new stories and improvements to the region. There're new player characters, an expanded regional Pokédex, a new starting town, and even a few new gym leaders.
I know what you're thinking: "Story? In a Pokémon game? You must be off your nut!" I think that it's a great idea. Story has always been the weakest link in a Pokémon game, and the developers decided to improve upon it. This has led to some mixed results, however: the game is a bit slower in the beginning and it's a lot more linear. However, the story aspect is improving quite a bit.
As for the designs, every generation had some good ones and some dumb ones. Generation 1 had the awesomeness that is Charizard and the it's-just-three-of-the-first-form-ness Magneton. Gen 2 had Umbreon (awesome), but also Ledyba (dumb). Gen 3 had Absol (cool), but also Volbeat (not cool). Gen 4 had Empoleon (yay), but also Budew (nay). Gen 5 had Galvantula, one of my favourite Pokémon, but it had Alomomola, one of my least favourite.
Gen 5 brought a lot to the table. From streamlined interface to quickened battle pace, from monthly seasonal changes which add to the time mechanics to giving Pokémon interesting new moves and abilities to play with. It's better than it ever was. The only thing that I disliked in 5th Gen was the linearity. I, for one, am extremely excited for B2/W2.