The puzzles were really well thought-out! I had so much trouble near the end until I realized I could just push the gem into a different position. The perspectives got the job done for the theme, and you adhered to the palette very well. Interesting designs.
The audio element was also polished more than I expected. You kept the visuals very simple, but it paid off in making sure the rest of the game was polished. Sometimes, less really is more. A tutorial or more in-depth description might be necessary. Also maybe add one final hard level, since 19 is an interesting spot to leave things on.