Saw the 2D version at the weekend. Can't last more than 5 minutes with those glasses on as it gives me a headache, so didn't even consider the 3D version for 160+ minutes.
In 2D the film was very good. I didn't find it gripping at the start, though it got a lot better as it went on - so much so that I would see it again in the cinema if I could get away with it. I took the kids who thought it was the best film they'd ever seen.
I did think that some of the spaceships and the robots (or "Heavy Metal Exoskeletal War Machines"!) were reminiscent of "Aliens". And Sigourney Weaver!
Definately one to see in the cinema, and 3D if you can.