Ah gotcha - I'll have to try it with a controller!
I think what stands out the most to me in terms of art was the first enemy you come across - the little bug guys that leap at you. They felt out of place, but that might've just been the animations, or maybe a lack of detail compared to the player character? I dunno. The room tiles I think would help alot - some of the dirt/stone details looked weird when some of it is just like, a thin line instead of chunky pixels.