Choose from 15 different levels, going from easy to very hard. The levels look plain, just a bunch of squares arranged in different patterns, creating a maze of sorts with entry points at the top of your screen and exit points at the bottom. You must place colorful, flashing towers – with names like GreenBall, BluePip and RedZip – in strategic squares to fight off the alien invaders. Each tower costs you money, and you have a limited amount. You’ll need to destroy some invaders to build up your savings.

Retro Defense goes for a real retro look and feel, and succeeds. The marching aliens are straight out of ’80s arcade games. And, the synthesized sound effects and vibrating shoot-outs complete the picture.

You can play for hours. The alien attackers get stronger, and move faster. You’ll need to buy more towers and tower upgrades to stop them from escaping the mazes. Before you move to the next level, you’ll need to stop 30 waves of aliens, and that’s not easy. Other tower defense games, like Fun Towers, feature lively graphics, but for flashback strategy fun, you can’t beat Retro Defense.