I've played one of the PS2 titles (the last game to have 'Ding' in it) and both Vegas games.
I enjoyed all of them, although I muched prefered Vegas 2 since I could unlock weapons *outside* of multiplayer. (Forgive me if I'm wrong, but IIRC, you could only unlock new weapons in Vegas1 in multiplayer)
I still play it, when I need a break. The terrorist hunt feature allows for some really good, short games. Easy to play a really quick game.
I'd love another Rainbow game (although I'd like to leave Vegas behind...)