So I jumped in and bought Red Alert 3...

[skace]

Now that I've played the game, the CO-OP is freaking amazing. I haven't had any issues with controls or AI, in fact if you set way points for units, you can transition them from ground to flying and they will update their path while continuing down it (for instance, a land unit is produced and creates a path to it's waypoint, you select that unit and transform it into a flying unit and it then updates its path to a direct route to the waypoint without having to be resubmitted).