After finishing Mario Galaxy, I decided to check gamerankings to see if there are any 3-d platformers for the 360. They listed very few. But one of the higher scoring ones is
Marble Blast Ultra. It's a Live game, so I thought I'd try it out. Holy crap that game is fun as hell. I was up until 2:30 playing the game last night, even though I had to get up at 7 am. I'm sure it's just the initial fun factor and it will get old a lot sooner than, e.g., GH or Mario Galaxy. But that's one of the best $5 (or however much Live games cost) I've ever spent on a video game. Seriously addicting game.