I liked that a certain atmosphere came across; it all seemed to fit together somehow.
But there were no sound effects,
and you have to use W and S to go up and down stairs—something I didn't figure out at first... it was pretty weird.
Also, sometimes I’d get stun-locked by an enemy after getting hit and lose several lives at once... and the boss fight is a nice idea, but I could just stand there AFK and wait most of the time—for instance, because the spikes don't spawn right under you.
As far as I could tell, I just had to wait for the countdown to finish to win, regardless of whether I actually hit the boss or not... but otherwise, it was nice ^^