From what I see, the game looks as to CoD4 360 as Rock Band Wii to Rock Band 360.
They look identical from a distance, coming up closer you will notice a lower resolution, and aliasing.
As well as some bad texture spots.
Still looks good though :D
I own all of lastgen systems as of October 2008. (Finally got a Dreamcast)
I own every currentgen system except PS3.