Loved it! A really challenging game that keeps you on your toes. You can't rest for a moment because enemies are swarming in from all corners! It reminds me of OSU in the way that you have to take in information at a very fast rate while reacting with very precise mouse movements. I saw it on the GMTK stream and was determined to do better than him. My highscore is 92 so far, but I'm sure I can do better than that.
The thing that kills me the most is if I'm on a good run, the screen is so full of dead bodies that it's hard to see which enemies are still alive and which are dead. But that also adds to the challenge at the same time, because I need to detect movement better, so it's not a criticism per se.
One thing I would like to see different is that after you die to not have to reset to the main menu, but to just have a 1-click respawn. Since you die pretty quick and often, it becomes tedious to sit through those 3 screens every time. I definitely don't think the design was bad or anything though. In my opinion it's geared towards a specific fast play style and while things could be added to make it a bit more forgiving, I personally enjoy the hardcore nature of it.
Also please add a highscore server or something! I'd love to compete against friends in a game like this. I think it has a very competitive nature to it and I'd love to score off against other people.
EDIT: 135!! Come at me nerds!!