A bit easy..
Didn't even used my special attacks. like space and num: 1,2,3,4. No sorry I just upgrades my magnet, firepower and some hull and speed. Not even maxed out! And I beated the game like a cake walk. You know why? The bosses are almost the same they spawn fire exact the same like all the bosses they only look different. AI was OK but damn sometimes the normal battles where easier than the bossbattles LOL you dodge those bullets so easy (bosses) Loves the upgrade system though, and the graphics and music. That is also the ONLY reason I would still give this a 10 and a 5. Game looks awesome, so I will comment you to really make a sequel with more and deathlier aliens/badguys. If you do that you got yourself an awesome adicting game. Hope you make a sequel :D!!! Fun game though really. I played it out so... that says at least something.
Well... long message, sorry for that. Peace out. ^_~