Really, fun! Perhaps a tiny bit slow but it probably speeds up later on, I actually got stuck on a level where I beat all of the enemies but then the doors didn't open :/ I got to like level 9 or so when that happened. The upgrades are simple but effective. I like the atmosphere and the gameplay is overall really fun.
A few issues besides the bug is that I didn't know the controls, I didn't feel like they were super easily communicated to me but I figured most of them out after a few levels. I saw something about a time stop but couldn't figure out how to do it. I saw that right clicking was like a sword or something? I only figured it out on the last level and never was able to use it. I also saw something about a dash in the upgrade tree but couldn't figure out how to do that either. Maybe a brief tutorial just quickly going over the moves in a fun way would be nice.