You play as American Marines and Red Army, and fight against the Germans and the Japs. The Jap missions are hands down the hardest since you can't see crap when fighting them.
You should try renting it maybe and give it a shot.
kind of, but there are some noticable differences.
I think the online play is a little easier all around, the maps are bigger, there are a few more game modes, the graphics are about the same, this one does use smoke and fire pretty well. There is much more blood and gore, limbs get blown off, heads get shot off, blood spurts everywhere, etc. The weapons are ofcourse not quite as good given the times when this game takes place, but so far I find the LMGs and the SMGs to be better than COD4's. There are also more challenges this time around so that helps you with ranking up and when you prestige you get to add on additional custom classes for your weapons (ie custom classes 6-10 are unlockable via prestigeing)
The single player campaign is pretty decent, so far I liked the story in COD4 better than this, but I haven't gotten to the end of the campaing yet, so the jury isn't fully in yet.
Nope. Everything I've read about the new one says it falls short of CoD4. They are saying that there are no improvements other than a change of scenery.