I have it, and have beaten the SP already. It's a little on the short side IMO, but well worth it. Some of the missions just had parts that were frustrating with how difficult they were, namely the one solo mission.
The MP loads up a lot faster than the previous game did and the maps look better in MP as well now. Unfortunately, I do not like what they decided to do with ranked matches. They limited Team DM to only have one respawn per round. Meaning, Team DM matches typically last 5 minutes or less. There's a good chance you'll be searching and idling in a pre-match lobby for longer than the match duration!
I believe only one (or two?) ranked MP modes have the option for infinite respawns or higher than 1 respawn per round. I personally find that to be a fat load of BS and so do others.
It is nice how they do have the ranking system carried over into SP though. So you can rank up and get new weapons/armor just from playing the SP game, so you do not have to play MP to get those items. And your created character is used throughout both SP and MP.
I'm enjoying the game, but there are a few glaring glitches (slowdown, clipping issues with guns, one hard lock up during a rather glass filled double grenade explosion during online co-op, and an instance where an enemy was able to walk on a wall...) and some lacking MP compared to the first. I'm awaiting a patch that will hopefully address my concerns. All in all though, I am having a lot of fun with the game.