It's super fun to play, and it definitely felt like a mad dash to the exit, but it's not necessarily difficult... enemies were kind of basic, and I wished there was a bit more variety.
I think maybe changing your HP to a max of 80 would make it much harder, but still fair. And, having some more enemy variants would be nice. One could be an enemy that doesn't deal a lot of damage, but always spawns in groups so it can overwhelm the player.
But, those are just my thoughts! It's still a fun game with a cool concept, I just wish it was a little bit harder /: Good job though!