Really nice aesthetic and the controls feel good. I was really impressed by the introduction cutscene and the interesting behaviour of the enemies. (Especially the bats).
As far as negatives, I did find the difficulty to be a bit much. I possibly missed some upgrades that would make things easier, but at some point I was just running past enemies because I knew I would die in two hits. I stopped playing when I got to the purple (I think key shaped) item, and fell in a spike pit before I could grab it due to the darkness. That felt quite unfair.
Despite that, I think this is an excellent effort for a month long prototype. With the difficultly smoothed out, this could be a really cool game if you continue it. (And I hope you do!)