Here's another recommendation for COD, its the first shooter I've even played through and I'm on the expansion pack now. Very cinematic sequences during these games, and there are some real adrenaline pounding moments, and it's a great game despite some of the quirks you get due to the scripted nature of the game. Expansion seems a hell of a lot harder than the first game, and in the expansion there are points where the enemies infinitely respawn and you just have to advance, which is irritating but doesn't really hurt the game much to be honest. It also seems like your totally useless squad members from the original are slightly more useful and actually shoot stuff in the expansion instead of quickly and bravely comitting suicide. Some of them also appear to be unkillable, but that may be because I'm on one of the easier difficulty levels. In COD2, they apparently made it so there are no health packs, but instead you regenerate health when behind cover, which I think is a huge mistake. It really takes away the most intense moments in COD, which are win you are down to so little health one hit from anything will kill you, and you've got to find a way to clear out a building or go around a corner not knowing what's there.
Edit: Or find a way to take out a tank before it blows up the wall you're hiding behind.