Watching the Xbox presentation. I missed the first half of it, so I'm going back to watch the Halo and Rare trailers, at least.

Out of the second half, the highlight for me was Psychonauts 2.

I'm not up to date on Halo by any means (I haven't played 1, 2, or 5, and I didn't play much of ODST), but the grappling hook looks new and useful. The map definitely seems like it will help.

Psychonauts 2 - Brain in a Jar Trailer