Very neat game! Some polishing tips:
- The start button clickable area is too small and to the left
- After 10 minutes things go a little more crazy
- The timer wraps to a second line
- The whole screen may shake and the player may be off-center-screen
- After 15 minutes there are just huge clumps of enemies stuck out in the open. Sometimes they break loose, but a lot of them are just stuck for a while.