Really nice! Cool graphics, fast-paced action, plays and controls fluently, it makes me wanna push onward to get more and more upgrades and that's a good thing! Only thing I'd suggest at this point is to let shield drops appear a little bit more often. I now played around 20 minutes and only then (when I died, sadly) a shield drop appeared. I know there's a also an upgrade to increase that, but I feel it's not nearly enough currently.
But other than that, really cool game!