Cool game. The music is good and I like the background. The idea of shooting into the center is neat and well thought out - the lasers that shoot along the edges are a good way to force the player to move around the arena. I think an interesting thing to add if you extended this would be enemies that can only be hit from certain directions. Though the directional controls can be a bit confusing, I can't think of way to do them better.
Also, the binary score counter is interesting but a bit hard to read at a glance. My best score was 1011001 - er, 89.