Just Leave Things Alone!
OK, flaming over. It is space invaders, but with 3D aliens, some extra weapons and bosses. This has, basically ruined the game by over complicating it. Although it doesn't sound too complicated, remember this is space invaders we're talking about. The oringinal bleep bleep version was a lot better.
In short why bother buying this, when you can just search for it on Google and get millions of free flash games that exactly mimic the original.