This is a neat little concept that feels like it could definitely be expanded on. My one big complaint is that, at least in the web version, the in game cursor lagged behind my actual mouse movements a lot, which made the whole thing harder than I felt like it should have been, and for the wrong reasons.
Edit: I thought of one more sort of criticism. With such tight timing, I needed to focus on the stuff on the screen I needed to interact with, which meant I rarely had the chance to read the flavor text on the top or really take in the enemy sprites.
But even with those, I still enjoyed myself and would be interested in seeing more.