I know I'm not the only one excited about Vegas 2, heck it's the second highest in pre-order sales currently. I played a ton of the first Vegas.
I played even more of the co-op mode (mostly split-screen). However, there was always something missing. What was it? You can probably say it with me. Story.
Where was the story in co-op mode? It was stripped down as if to say, what happens in Vegas stays in Vegas... single player mode. Well, fear not, Vegas 2 is quoted as bringing the full, uncut story from single player directly to the co-op, as it should be. For all you co-operators, that means you won't have to play through the games single player campaign just to understand why you're chasing some chick terrorist.
There's an Ubisoft Developer's Diary video up on the official Rainbow Six Vegas site explaining some of the co-op details. They also mention a sweet "jump in, jump out" feature. That way, you can, let's say, jump out, if a scenario looks a little too hairy, and after your friend has taken care of all the terrorist, you can jump back in to share the credit. All in all this game looks like it might just set the next standard for co-op.