A solid game with good animations, good controls and devilish level design. On contrary to many puzzle games this one focuses on the execution of the puzzle and not the resolution itself.
Remembering where things are is half the work, the other half if knowing how far can you jump, push your boxes and where the character fits.
The mechanic gets a bit tiresome later, maybe try complementing it with other mechanics to add some variety to the levels. Other than that, the game is tight and challenging, as good puzzles games should be.