I'm generally a big fan of your games, but have to admit I didn't really get this one (sorry). I first tried playing it according to the instructions, waiting for the enemy's damage circle to go down and then pass through it, pressing space to damage it and in doing so always seemed to take more damage than I was dealing. In the end I beat it by going straight towards it and spamming the space bar, which is kind of the opposite of what you seemed to be going for when you say, "something you deal with over time rather than instantly."
Love the particle effects with square particles and the subtle graphical effects you put in though, taking some simple shapes and making them more interesting.