This was fun. I like that you show the spawn points, but also have them spread enough that you'can't just sit at the spawn point to attack as they come out. I got to level 3. The new enemies spawning as you progressed kept things fresh. I did find that I could circle around them and get them into a group where I could just hit the outer ones and move away before they hit back. It wasn't perfect, but was decently effective.
I was not able to use any of the specials. I pressed the buttons, but nothing seemed to happen. There were arrows above them that looked like buttons, but clicking on those did nothing. I did need to play in fullscreen to see them and much of the game, so that may be part of the issue.