Great game. 5/5
I just stuck with the shield thing and from time to time upgraded the turret. Ended with 10 in engine, ~140 in shield and 60 in turret. The boss was hard enough. It killed me about 5-10 times :P
I think that there should be some cards that you can get from games. The challenge will stay forever (or for a very long time), will be in the difficulty of a hard/impossible badge, will be slightly better than the other cards and will be unique from that specific game. Same inside the game (make some bot opponents that will give special cards and such).
That's my suggestion :)
Would be better if it had a "save" and "mute" buttons, and if it'd be somehwat harder. Oh, and the darkness was just fine. You people should probably make your screen brighter.
Try my level. The code is long so I've put it in my shouts. It's not easy, but not too hard either. Anyhow, it's not one of those levels that you can finish on the first time ;)
 "Ether Cannon"){kind=icon}
 "Scope: First Blood"){kind=icon}
 "Clear Vision 2"){kind=icon}
 "Cirplosion"){kind=icon}
 "intrusion"){kind=icon}
 "Asteroids Revenge III - Crash to Survive"){kind=icon}
 "Luminara"){kind=icon}
 "Amorphous+"){kind=icon}
 "Tangerine Panic!"){kind=icon}
 "B29 Assault"){kind=icon}
 "Army of Destruction"){kind=icon}
 "Mezzo: Winter Edition"){kind=icon}
 "Tactical Assassin 2"){kind=icon}
 "Warlords: Call to Arms"){kind=icon}
 "Kongai"){kind=icon}
 "Free Rider 2"){kind=icon}
 "The Last Stand 2"){kind=icon}