Should you be one of the few people on the planet able to get your hands on a 360, Talk Xbox has a preview of the arcade portion of the Xbox Live service:
The games on XBLA (Xbox Live Arcade) run the gamut from heavily revamped coin-op games to original indie titles and everything else in between. And when I say coin-op, I don’t mean Bubble Bobble. I’m talking Smash TV, ported from the original ROM code with updated sprites and Xbox Live multiplayer. I’m talking the original Gauntlet, again ported from the original ROM code, and again with Xbox Live multiplayer. I’m talking games from studios such as Ubisoft, Midway, and EA, all of which have submitted game concepts for approval.-- Hands-On Preview: Xbox Live Arcade
It also mentions that for the first time in the industry, an indie title is available at launch for a major console. Congrats to Marble Blast Ultra for getting in one the ground floor.