Great
I got all the achievements and made it to top 40 on the all time list! Whoo! Great game. The biggest complaint that I have is that the recharge time goes up as you upgrade your energy reserves. It's back asswards that the more you upgrade, the more you are punished for letting your energy hit zero, because you are shieldless until your energy hits 100% again. I feel like it would be much better if the recharge rate from 0-100% stayed the same regardless of how much energy your ship can hold. Another thing that bugged me was that it got somewhat difficult to see your ship when the screen got busy (around level 20 or so). The ship should be more distinctive. Finally, I think that it would make more sense if you went straight to teh upgrade screen when you died, rather than going all teh way back to the menu screen. Not a big deal, but clicking through the instruction screen every time got a little annoying.
Otherwise, fantastic job. I hope to see a sequel, hopefully with more upgrades and enemy types and maybe even different ships to choose from.