This is a pretty nice game! Visuals are fantastic, and I like the soundtrack a lot too. The gameplay itself is pretty fun! I'd agree that the boss difficulty was pretty low (I was able to pretty much stand still and mash the attack button to win)
There was a section too where the spikes were able to hit me through the ground I think. I'd also maybe recommend letting the grim reaper fit on one screen, cause right now he's too big.
The story seems pretty interesting too, I'd like to see it expanded on.