my favorite coop game of all time would have to be command and conquer red alert for the PSX. It was the game that made my brother and I purchase another PSX and extension cable for to play together via system link. We would set up skirmishes on a particular map that featured an almost tic tac toe play field and then build up our defenses while we wait for the AI to onslaught us. We spent many an hour each day playing until we'd start to fall asleep in the early mornings. Good times.