I take back what I said about the multiplayer... this thing is a mess. I'll list all the problems I've had with it, starting with the boosting problem.
You usually get kicked for idling, unless you are the host... so in order to get their 25 wins and 100 matches achievements, people will keep joining until they get host, and then just idle. They won't even join the actual game, but the game considers them as part of a team... one host was away for 3 hours when I checked his gamer card.
It makes the teams uneven, almost ALWAYS 6 vs 5... and it's 9 times out of 10 that team who is missing the extra man ends up losing. This, coupled with the problems I've listed below, have pretty much rendered this game to be a game you'll play online just for the easier achievements and move on.
In addition to that, the other problems include the lag, the glitches, the SEVERE lack of maps (there are THREE maps for MP... that's it... dead serious), the leveling system that is there for no reason (seriously, what the hell is it for?), the extremely unbalanced classes (Revert + Proximity Mine = instant kill, always. No exceptions), and Raven has messed up another MP that could have been somewhat decent. Initially, the MP is great, but man do the cracks start to show after a few hours. It's a shame, it's pretty unique and I love the class based system even if it is unbalanced.
Three maps... seriously? Why even bother making a multiplayer mode? To sell us more maps later? Raven and Activision completely over estimated the MP in this game because nobody is going to care.
I hate to completely flip flop on what I said previously, but I can't believe it's got three maps and this many problems... my first post was only after playing it for about 30 minutes, and I still hadn't seen any of these problems. I haven't played the single player yet but I'm glad I got this for $25 and not the full $60.
It's super late, so if anyone wants me to go into more detail tomorrow, I'll be glad to. I just really hope the single player is as awesome as everyone says.