Monday Game: Alien Annihilator

This game is a bit like Asteroids, except that destroying asteroids isn't the main point; destroying the enemy ship is. If you shoot asteroids, you get extra health points. If they hit you, you lose some. There are also helpful power-ups. But your enemy can use them, too, so get to them as quickly as possible.

One odd thing: when you lose a level, text appears that says, "Having trouble beating a level? Try replaying the level you just beat to gain more points so you can buy upgrades." The trouble? Once you're on a new level, you can't go back. You can only replay the level you're already on—the one you're having trouble beating. So if you're having trouble beating a level, you're outta luck, short of starting over.

Apart from that, it's a pretty enjoyable game.