I played it for a while and thought "yo, is cool" and promptly plunked down twenty five PayPalBucks, buying myself a legit copy form their website.
Basically, you mine minerals, collect energy from the sun, and you build weapons to destroy the bad guys. They attack in waves, first one, then several, then screens full of flying saucers and other nasties will swarm your little outpost.
You only have 5 kinds of buildings available, one of which can be upgraded to two kinds of missile launcher. This paucity of unit types makes the game very easy to learn: Gather, link and defend. The fun lies in trying to survive longer and longer in each successive game, and it's not easy. At first I was happy to survive five rounds, then I was doing twenty, thirty, and finally fourty rounds!!
It's good fun, and it looks good too: