Mario - still going strong.
Super Mario Galaxy 2 follows one of the strongest games available on the Wii - and probably one of the most well made games of all time. The first Super Mario Galaxy took everything you know and love about 3D platforming and Mario games and took it to the next level with brilliant level design, stellar visuals and music, and simple, yet effective controls. Following that act has to be one of the most difficult things you could do, but of course Nintendo pulled out something that is most definitely a sequel, but is surprisingly new and innovative.
The key to the Galaxy series is level design, and I don't think I could find a game that does it better. Everything about each level is so specifically designed, and nearly every single level is distinct from every other - yet they are almost universally enjoyable. The addition of Yoshi with his various diet-based powers (float like a balloon, run up walls at top speed, reveal hidden platforms) adds variety on top of what is already an incredibly varied game. Other levels range from Super Monkey Ball esque obstacle courses to stages where the arrangement of land changes with a specific rhythm to some standard platforming sequences and beyond. Even if you don't enjoy every level, you can rest assured that the next one will be completely different.
Galaxy 2 also happens to control extremely well, just as the first game did. If you've played a 3D Mario game since Mario 64, you should be pretty familiar with the basics of the controls, and you'll be flipping, long-jumping, and ground-pounding your way through the levels with style from the start. Of course the visuals and soundtrack are also very strong - this game looks and sounds absolutely beautiful.
From collecting your first star to the final epic boss fight, you'll see more variation in this one game than you'll find across many entire franchises. And don't be fooled by this game's cartoony look, or the fact that Nintendo made it - there are some serious challenges waiting for anyone who wants to take a crack at them. Anyone who has ever enjoyed a platformer would be crazy to miss this one, no matter your skill level.