Very small touch, but I like the little animated line when the player moves. It really gives weight to the movement. And you nailed the speed and animation of the movement too. It just feels good. Hard to articulate!
As far as the gameplay, I don't think it's the most engaging. For the first couple levels, I felt like I was just wandering around and hoping I'd run into the keys I needed to progress. The puzzle in the third one had a bit more to it. Do more things like that I think!
Also just to help with getting lost, it might be nice to have a little minimap of where the player has been. It could be hidden behind fog of war (something like the Mystery Dungeon games might be cool).