Absolutely try some demos. One of the better things about the new and improved xbox live are the demos. They're great. It's so nice to be able to see if a game's a stinker before dropping $60 on it at the Wal*Mart.
Dead Rising is sitting in my machine right now and my next purchase is probably going to be either Gears of War (no demo
) or F.E.A.R. (killer demo
)
As for recommendations... Oblivion is my current obsession, but I can recommend the new Marvel game, Splinter Cell: Double Agent and Hitman: Blood Money all of which spent an inordinate amount of time in my machine.