My first thought after playing Super Mario Galaxy 2 for the first few hours was that Nintendo was kind of being a jerk about the whole thing. It's much harder to nail a satisfying game mechanic—whether it's in 2D or 3D—than people understand. Nintendo constantly shows you something amazing and masterfully produced, and just when you've gotten over being amazed at how well it plays, the game throws it away and offers up something else, equally good.
Saying this is Nintendo at its platforming best is an understatement. This is the equivalent of a baseball player hitting nothing but home runs for an entire four-game series, calling his shots Babe-Ruth-style before each swing. Nintendo plays with the genre like there is nothing at stake, doing incredible things with it as if it's simply a decision to make a game this good.
So what do you have to do to earn these stars? Everything! Fight bosses, platform in 2D and 3D... you'll swim, fly, float, and fall. You'll need to hurry, you'll be forced to take your time. In some cases gravity will be your enemy and at other times it will be your ally. You'll meet friends from past games... and enemies too. Sometimes entire sections of the game will remind you of past Mario games. There is no way to describe the sheer joyous exploration of the game, nor how surprising many of the moments are, without playing it yourself. We could list a variety of the levels, but why take away the fun of discovery?
Mario is given a huge number of moves to interact with his world. He can jump, grab, back-flip, triple-jump, long jump, and wall-jump. There are circumstances where he can fly, tunnel, and roll. He can grab items, ice-skate, climb, and butt-stomp on both enemies and the environment.
This is, thus far, the peak of what platforming can offer.
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