Anyone play Battlefield 2 on the PS2 I think it was? You could look at any allied character on the battlefield and hit a button and you'd take over control of the character. So you could be a soldier on the ground being pinned down by a machine gun nest, look up to an allied helicopter, hit the button, become the pilot, launch missiles at the nest, then look down to a tank, become the driver, then back to the soldier, etc,... So much fun! I think they called it 'hotswap' or something.

Any game devs: This was the single most fun mechanic I've played in years. Please please please make an FPS where you can hotswap between characters like that. For some reason apparently this awesome feature didn't even make it into the PC version of the game. I'd love to play a game with that mechanic again.