I only had 11 months with the 360, but I played it a fair amount. I think I'll go with Crackdown. One of my favs from last gen, 360 or otherwise. Somehow, I didn't like PGR 3 as much as PGR 2, or even, strictly in terms of car handling, as much as PGR, but it was still great. Was pretty lukewarm on Kameo and Viva Pinata. I REALLY never got Viva. I did try, but likened it to a digital fish tank. That's all I can think of within the confines of the op stipulations and my limited time with the console.
Chinese food for breakfast