So far I've not recognized any of the multiplayer maps, and the multiplayer setup is a little weird, as each player chooses their gun and player. Oddjob is still a cheap little midget (but allows for more BOOM! HEADSHOT!) Proximity mines can't be flashbanged. Only shot or blown with other explosives, so well placed proxes will be difficult to circumvent.
It has a few new missions, and some classics, which are definitely different, because the maps are so different. Multi options are somewhat limited regarding gametype and maps. I assume more are locked/hidden. I'd like to see OHKO mode again. Some options are just silly. The "No camp" mode where you die after being stationary for more than a few seconds is nice, but the timer is too short. Not even enough time to check the scores. You'll die within three or so seconds. It lasts longer if you've run a long time, but most I've lived was about six seconds. I think it needs to be about 10-15. Another option is "singularity" mode, where players explode if they touch each other. Just silly.
Paintball mode is available, as are options to remove radar and such.
I'll be waiting on a save file online to unlock some more stuff. (With Black Ops coming in a few days, won't have much time to invest in unlocking things myself.)