Judging by the demo and a bunch of gameplay videos Vegas it's not even a particularly good action game in my opinion. The presentation is admittedly pretty nice but the gameplay feels like either a seriously dumbed down Ravenshield or a boring, undynamic Gears of War.
Just corridor after corridor full of enemies waiting for you to come for them.
In this regard the game feels a bit like an uninspired, fan-made singleplayer campaign for a real game.
The presentation is really cool at times though and the general gameplay (how cover works, how the weapons behave, etc.) is serviceable. Nothing special and not really fitting for a Rainbow Six game, but it's ok. The horrible level design (again, aside from the presentation!) dragged it down too much for me, however.
But if you liked it, good for you, of course.
Unfortunately there was no demo for Vegas 2 or I would have given it a chance.
I did like GRAW though (talking about the 360 version, just in case)!
And not just as "a game in its own right" either, but I think it was a fantastic sequel to Ghost Recon 2 and Summit Strike (xbox version) as well!
How those two stack up to GR1 and its expansions is another story, but GR2 -> GRAW made for a great sequel.
Enemies could have been less numerous and smarter instead, or at the very least more randomized but it was pretty enjoyable anyway. The behavior of the weapons was rather cool too. They felt heavy and dangerous.
The only part I really disliked were the gatling sequences but at least they kept them simple so you don't get stuck in one.