It was a really good game, I like the art style and the music. The only problem I see with this game is the lack of 8 directional movement. I think it would've been better if summoned minions started following you instead of patroling the area they spawned on. Also, there is no penalty for not killing enemies, and you can just ignore them and run to the exit.
I found a bug in which an enemy book became unkillable and started missing every single shot after I had one of my skeletons beat him.
Overall, it was pretty hard, but I really enjoyed it.