Don't get MLB 2k8!, I heard it's HORRIBLE on 360. Everything is too compressed and the graphics look like an original Xbox title. The full game couldn't fit on a DVD and needed to be compressed, so now it looks like doodoo.
I'd go with Army of Two.
That looked fairly good. Though I'm holding off on buying any further games until MGS 4 hits in June. Might give this one a shot through renting though.getting army of two 2day!
I'm hooked on Geometry Wars on X-Box Arcade/