I liked that the puzzles utilised the main mechanic in various clever ways and their solutions were reasonable. Each puzzle's short length allowed for faster experimentation with the puzzles as you can quickly set-up a certain state after restarting is. This reduced frustration when a failed state was achieved.
The introduction of new game mechanics was well paced. The music was pleasant to listen to and wasn't distracting. The graphics were simplistic, which I think adds to the charm of it.
The final puzzle felt slightly cheap as you wouldn't have fore-knowledge of the order the boxes would have moved, though it was a puzzle twist on the main mechanic.
Perhaps the only forms of improvement would be to add new mechanics or gimmicks. For example, a pause/play switch to halt/resume reversing; boxes that move slower or even skip steps when reversed. Though I think adding more gimmicks would ruin the current feel of the game.
A very well polished and pleasant puzzle game that can present a fair challenge.