I just played my first online co-op game. I was the player who chose the plays, controlled the QB, etc. My partner and I were the Vikings and we played against the Eagles. We ended up losing 17-14; I will admit, I missed the game tying field goal
I had loads of fun, it was really satisfying when you call a HB Toss and a human-controlled FB is clearing your path to daylight. Or a simple QB to WR touchdown pass from user to user is very satisfying as well.
However, the special camera that co-op mode uses kind of takes away from its fun factor. Playing defense is especially difficult, and so is kicking. The kicking arrow doesn't line up with the camera. Unless you play as a D-lineman or blitzing, playing defense is exceedingly difficult with the slow-panning camera.
In the next Madden, we should have an option to choose between the camera we have now or the standard camera that madden uses. A 3 on 3 or even 4 on 4 co-op mode would be awesome!