Great graphics and audio. The music gets repetitive though. Personally I don't like controls where the direction is set by holding a mouse, but I got used to it after a while. Sometimes I couldn't find any enemy and was randomly roaming. Maybe zooming out when moving faster could help, or some enemy indicators?
After the first upgrade I was losing health without any contact with anything. And there was a little lag on first explosion. Still a great game and I had a lot of fun!