Just fantastic!
As for the sound, well, I just can't even describe how wonderful it is. With the surround sound system I have, the game's audio completely envelopes me. The sound effects are so perfectly done: from the M16 to the car explosions, it's just phenominal.
The single player mission is a lot of fun and very engaging. You quickly get into it and feel the urgency of the missions. I'll admit, as a WWII fan, I was concerned about COD going to modern warfare. But, my fears were quickly put at rest when I jumped in. For one, the weapons are a whole lot cooler and exciting than the 60 year old versions available in previous installments. Besides that, there is a feel of a global threat that hits you right off the bat so you want to jump in and make a difference. The single player is short, but worth the ride.
The game really goes over the top with the online play. Honestly, I've always feared online play. I tried Halo 2 a few times online and just felt completely overmatched everytime. I'm not a sore loser, but, I hated getting slaughtered in that game. With COD4, I'm not sure if its the weapons and enviroments or if I'm just getting a little better at the FPS thing, but I can hold my own and that makes it very fun. The multiplayer maps are all great and different game modes are fantastic. You can be a loner and go for a simple free for all deathmatch or play some real team games like Domination or Search and Destroy.
I honestly can't get enough of this game. If you like FPS games and/or COD, you have to get this game.