It arrived yesterday and I haven't played it yet. A few friends have said its excellent. I'm still trying to finish gears 3. Got about 10 more achievements I need.
It's good gonzo! Campaign was excellent. Very short so worth doing on veteran to get the most out of it. New mode called extinction is also good. It's a 4 player coop mode that you and your team have to kill a load of aliens. Well worth the £40