Disappointingly tedious. Overlong passages where nothing happens, and no obvious storylines or mysteries to keep you in suspense while you're waiting (and waiting) for something to happen. Unfortunately there's barely a chuckle either as it takes its preposterous premise rather seriously.
It's mostly a western, but even the scifi elements are over-familiar. The Cloverfield alien blueprint is back (yawn), and their spaceships just look like spare ribs.
It's not a complete disaster. Daniel Craig is especially good and there's a twist you might not see coming (not a particularly good one though). It's not quite Twilight boring, but gets there at times. Not what you'd expect from the director of Iron Man.