This is sort of what I do with my brother - he's my wingman, or, as we put it, peripherals. While I get the guy in my sights, he ensures I didn't miss that guy who darted past me earlier. It is a good system, and we can then talk about it afterwards. Especially when I insist he's wrong and that he's an idiot, and promptly have my guts pulled out.
Karma can (and does) bite me.
But it has to work this way around. I can't focus on the puzzles that are too complex, or I miss a part and die, but my brother, while capable, isn't that great at multiple actions in games - in Brother in Arms, he would frequently forget to actually move his squad around.
Apache: Air Assault is a great one for this: The co-op offline is on one screen - player one moves the chopper, while P2 shoots the machine gun and rockets. But while the gun can be aimed by P2, the rockets must be lined up by P1, neccessetating a definite need for co-ordination. But it is worth it, when a convoy is in ashes behind you!