The game looks really good and I really like the sound effects. A and D instead of arrows is always appreciated but the game is fun anyways. The only problem I had (and one that I had on a similar game I made) is that you can easily get a bunch of points by staying a same place and pressing the space button every once in a while. Maybe make the bullets not destroyable.
Overall, a little game that is surprisingly fun and looks and feels good, but just with one problem.