Galaxy 2 Galaxy Kirby's Return to Dreamland (I'm still pretty early in it, but this is the most fun I've had with a game in a long while) NSMBWii Kirby's Epic Yarn Super Meat Boy Sonic Generations DKCReturns LittleBigPlanet
Rayman Origins probably ranks pretty well too, but I've only played a little of it... it was with three friends and it was totally rad, so I'll definitely get back to it sometime. There are a couple other Wii games that are probably good candidates that I still need to play properly too.
edit: forgot SMB.
-- For your SuperNiceDog. At least Kupo has class and doesn't MESSAGE the people -Dr Pizza
I'll let you know in a few months. I have a lot of catching up to do in this category.
Eh, hell, I'll show you what little I have so far though...
SMG NSMBWii Sonic Generations MM9 Sonic Colors NSMB
It's definitely been the best generation for at least 2D platformers since the 16-bit era, by the way. If all the 'retro is good' popular series hadn't secured that statement then the indie platformer extravaganza would have done it anyway.
The previous two generations were hellbent on evolving away from that style for the most part because "3D is in now, dammit; nobody wants that anymore." Enough gamer desire for some 2D lovin' finally started to deliver a few years ago and it's been on a great swing.
That said, on my dismally short list I still have Galaxy at the top. Nintendo really aced the 3D platforming thing with that one and most tell me the sequel is that much better.