It took me a while to figure out I could dash from mid-air. But after that it was pretty fun. And I got stuck where it looks like you have to go down, right, left and right to avoid spikes (except you can't change direction that many times)... unless I was supposed to go somewhere else before. I might have got lost in the dungeon. I've made lots of mistakes, but at least there's checkpoints, so I can try over and over. And the art made of squares look pretty nice.
I like the music too (could have wanted a slightly longer song, or perhaps having different songs played when you're outdoors and when you're in the dungeon, but I know it's one of those things that can be hard to get right in a small amount of time). As for sound effects, those are nice too. There's a sound for dashing and there's one for reaching a checkpoint. And if you die, you get back to the previous checkpoint, triggering its sound effect.
And the theme, I didn't see much of it. I felt like I was just falling further and further down, but maybe I didn't play through enough of the game.