i bought this today, and it's quite a fun game.
story isn't really what this is going for but it doesn't need to, it's just good clean shooting fun. trying to find different ways of killing enemies for skillpoints really adds to the enjoyment factor, cause it always makes you happy when you find something new
gameplay is pretty solid, not really anything negative to say about it.
there's some bugs in it though, in campaign, there's buddies with you, and it's happened several times now, when reaching some stairs, instead of going down them, this character would just continue walking on the same level... so he'd be walking up there in the air... happened like 3 times in the same chapter.
as far as multiplayer goes, it has like a horde mode called Anarchy, which is also good clean fun. played it with a friend and I had a blast, one thing though, mics should be used, I didn't have mine on and couldn't understand what the hell the other was saying... and you get more points if you teamkill someone, but without mics or understanding each other, it's pretty hard to figure out these team kills as you don't know what the other one is gonna do or wants to do... but other than that, it's great fun.