I know that some have already suggested Vegas 2 but lets not forget there was a first and the community for it is still going pretty strong. I would suggest staying away from Team Sharpshooter games though, people who complain about being spawn camped in COD probably either forgot or never played it, because trust me it makes the system in COD look like a masterpiece. Other than that I find the experience quite enjoyable and another perk about Vegas 1 is that the downloadable map/multiplayer packs are free on LIVE. The single player is above average however it can be unforgiving for those that will not adapt fast enough.
I can't in good conscience recommend Vegas 2 because I have not played it, if I did then I would give you an opinion. Most opinions I've heard are positive but I'll not sell you a house without looking inside first
I wouldn't really call COD4 a tactical shooter at least in the traditional sense and (even in team deathmatches) there does not seem to be too much of an emphasis on team work.
As with Vegas 2, I've not played any of the GRAW games but again I've mostly heard good things.