Warlords! Man, that game ruled. It's kinda hard to describe, but I guess it was sort of like a 4-player version of Reverse Breakout.
You're supposed to protect your own bricks by bouncing the ball off your shield - that little U shaped blob. The mechanics are similar to Pong and Breakout, but the big difference is that in addition to letting the ball bounce off your shield, you can hold down the fire button to "catch" the ball and release the button to "throw" it in any direction. If the ball manages to get through your bricks and hit your "knight" (that little weird shaped block thing), you're out. Last man standing wins the point.
This game is
amazing with 4-players. I didn't get to play it much, 'cause I didn't own an Atari myself... But every now and then, me, two friends, and this spoiled rotten asshole rich kid that no one really hung out with except to play his games (he had, like, every console ever) would gather around a big screen TV and get into some downright intense battles.