This is a hard game to rate. As Rainbow Six title it;s a total failure, it has little little realism, no pre-mission planning, the team got smaller, you have extremely limited control over them, the game got much easier, no more "one-hit and you die", it has regenerating health(Clancy must be having a heart attack :) ) and the whole game basically took tactical elements and threw them away and replaced them with fast-paced action. So if you loved Rainbow6 before, this one won't be loved for the same things.

Now. It's that bad if you treat is as separate game, without all the hopes and expectations fans of team Rainbow have. On it's own the game is quality shooter, the locations are good, the weapons are very nicely done, the enemy AI is pretty average, altough your team members AI is better, the shoot-outs look spectacular though and are fun to take part in. The game unfortunatelly is horribly unoptimized. It takes a beasty PC to run, and it doesn't look anywhere near as good to rationalize such performance. Especially textures are mediocre quality and the blood is seriously overdone. Animations are amazing though.

To sum up: horrible tactical shooter, very good arcade shooter that doesn't reach it's full potential because of rushed code.
If you wanted new Rogue Spear or Raven Shield forget about Vegas,but if your'e looking for fun shooter this might be just for you