Worth a rental if you're interested in campaign only.
On the whole this was good fun, let down by a poor final third. It's more of the tried-and-tested Gears gameplay, no problem there, and I enjoyed playing through quite a lot of the early levels with three other players and had good fun.
That said, I just felt that there wasn't much new in this game. It attempts more of a story, but really it's the usual clichéd stuff that passes for story in most games these days and really isn't anything special. There *are* a couple of touching moments in the game, a big one unexpectedly half-way through the game in particular that I won't spoil.
My main problem was with the last hour or two of the game. It's really just fighting through room after room up a tower, very regulation stuff, and it's like "press these three buttons, ok now go and press another couple of buttons," really nothing very exciting at all. The end boss is a doddle and totally unoriginal, and the ending is a little bit odd feeling.
Anyway overall although the gameplay is fine and nothing new, it's still reasonably fun, especially in co-op (although weirdly nobody joined me in the later levels) but I felt a lot of very interesting backstory and concepts weren't brought together very satisfyingly in the conclusion to the series. Gears 2 was best for me!