Absolutely fantastic! This felt like it was straight out of a super nintendo game with the sprite and tile work, the music and challenge! Just the right length of time as well.
I couldn't give up even when I saw you had to go backtrack for keys (Though thankfully it's not too hard to go in quickly and evaluate much of an area to see if the spot depicted on a mural is present) and I was eager to see things through to the end.
Very fun cliffhanger as well.
I look forward to a sequel!