Loved it
I absolutly love the 90's shooter style games, and you hit it perfectly with your own twist on it. The upgrade were great, although it often seemed like there were not enough points to go around. The accumulation of experience also seemed rather flawed. Having to fly around the screen constantly tring to pick them up while dodging fire was a slight pain, but also quite enjoyable. It added to the difficulty quite well. Difficult games are by far the best. As for performance, I had no less than 50fps throughout the game. Overall, you did a damn good job, but it could still use some tiny tweaks.