Very solid game, the difficulty progression was fine and the hidden chests weren't too obvious or too difficult to locate.
The one flaw I found in the excellent level design was the moving platforms, there were no walls or indicators to show when they would switch direction which made puzzles involving traversing those fairly annoying.
Secondly, the sound and music was nice although I don't think it really fit the pixel-visual theme you went for. The evil laugh in particular whenever the rooms went dark or the mimic chest I found, sounded more comical than anything, but maybe that was what you were going for.
Lastly I was a little confused by the game telling me to press R to restart an entire level when I could just press C to return to my last checkpoint, presumably R is intended for when you get stuck but even then I wouldn't expect it to take me back to the very beginning of a level.
Despite these gripes, the game itself is excellent, the controls are fine, it plays fine, and the challenges and general concept of navigating in the dark was handled perfectly so that it was never frustrating to figure out my way.