I've never played COD4 MP, so I wouldn't know what they're like, I know a few of the maps from them being in the Stimulus, and one or two from watching old SeaNanners and Hutch videos, there's one which could be fun from COD4, which is the second to last level I believe of the SP game, the one where you've got to plant the C4 on the armoured trucks and it's just a big open yard with 2 missile bays at the end of it.
I would also like them to put into it more merc options too (as in merc dom, snd, demo etc) as that'd make life so much more enjoyable playing the game. But here's dreaming.