3. Off The Wall
Atari's smash hit Pong led to several follow-ups on the 2600. There was Video Olympics, which used modified versions of Pong to emulate ice hockey and soccer and foozball. Breakout and Super Breakout were essentially one-player Pong only the opponent was a wall you chipped away at piece by piece. All of these added a few twists to the Pong format of hitting a ball with a line, but Off The Wall went crazy with additions. It even added story.
In Off The Wall you were a kung fu monk battering down the Great Wall to get at a caterpillar-like dragon while a crow attempted to block your ball, but also dropped power-ups on you. Those power-ups included a magnet that let you steer the ball and a detonator that turned it explosive, knocking chunks of wall-pixels away with riotous leaps of the score meter. The score made a clattering din as it ticked upwards in surprised bursts, a glorious cacophony. There was also a zigzag power-up that sent the ball spiralling, and according to the manual this could help you get past the crow though in practice it just made the ball harder to hit and was a curse that should have been banned by law.
Other games added complications to Pong but Off The Wall piled mountains of stuff on top of its simple elegance to create something mad and ornate, which should not have worked but absolutely did.