I've been playing with the engine, just to see what you can and can't do, and where you can and can't go in game. in the single player. If you bring through a Jaw guided missile from road rage, then you can shoot out the lab windows (top floor), in Lab Rat, and then blow the computer up from outside - the crane is a good spot - with the jaw, to face the helicopter from the rest of the level. When you have shot the gunner, and it "parks", where you normally can't see it, use the visor to spot a couple on the roof, who need shooting, before the chopper circles around, ready for another go.
Has anyone managed to get on the roof yet?
Any other interesting variations on any of the levels?
Have you noticed the ceph don't like walking on the boring tentacle things? This makes life easier if you want to stay and collect nano points before moving on to the next bit, when you're in an area that keeps spawning ceph.