So fun! But...
Don't take these the wrong way. I mean, I got all the achievements in this game, it's so fun. But,the only things wrong with it are the shortness of the game, and how easy it is! I think I've only died about six times (because of tiny and arsenal slugs/metal, flying things).
I have a couple recommendations, though. Make the game longer and more difficult, ADD MULTIPLAYER (PLEASE?!?), and port to either the Nintendo DSi/3DS or PSP (trust me, this game would be great for handhelds everywhere, especially if you include Multiplayer and the achievements along with it).