Nice clone, but...
...the game has a couple serious flaws which turn it from a lot of fun into a real pain really, REALLY fast. It starts fun, and is an excellent clone of the whole Geometry Wars style of game. But, the issues which really need to be dealt with are these:
A) Playfield's too small. In a game like this, you REALLY need to see the whole playfield -- the action gets too frenetic too fast to rely on a radar. You could either shrink everything (which would be my choice, the graphics are HUGE as it is) or simply resize the game's resolution.
B) Cost of powerups. As LOTS of other people have noticed, health starts cheap, but gets expensive REALLY fast. Either cap its cost at something reasonable, or make it a uniform cost. Also, making you re-buy shot speed whenever you upgrade your weapon? Feels like insult-to-injury, and made me not want to buy it at all.
C) Control. Some people like mouse control, but I have great difficulty managing it. Please offer a WASD-to-move, arrows-to-shoot method.
Address these things, and you've got a real winner!