This is the best kind of puzzle game: simple, yet difficult. The puzzles always contains very few elements but they have to be cleverly used and, in the end, it feels very rewarding to solve them.

The main mechanic revolves around the recursion principle. Most puzzles contains chests that links different rooms together. When you enter a chest, you don't just move to a different room, the room you move to gets created at the same time and then destroyed when you leave it. You basically go to rooms inside rooms inside rooms etc...
Otherwise, puzzles also contains rocks you can climb to go higher, keys to open door and a few other item that only appears late in the game. There are not many elements but this is enough to create some really compelling puzzle that forces the player to exploit all the possibilities of recursion. In the end, you really feel like you are mastering recursion. To quote the game: "The worst part is, it's starting to seem like it makes sense".

The store page is a bit outdated since the game now contains ~100 puzzles with a bonus ~25 levels you can get to by creating "paradoxes" in some levels. It took me about 16 hours to finish everything with the help of a guide for some of the most difficult part and i'd say that around 95% of the puzzles where really satisfying to solve so i'd say the current price is definitely worth it for this game if you're inetrested in it.

Otherwise, the music is great, the graphism are functionnal and the controls are ok. Thankfully, you don't need to do any difficult platforming.