Nice game with simple graphics.
Although I got stuck somewhere and wasn't sure if this was the end or if I did something wrong.
And since there were no checkpoints restarting the entire level was the only way to go back.
I think most people below make really good points on how to make the game feel nicer.
- A bigger viewport of the camera
- Maybe adding the how-to as text in-game inside the level makes it feel less like a wall of text as well as only telling the information when it's visually present and needed.
- remove or reduce the effect of the trail and maybe add some slight particle system at the bottom of the player instead
- and maybe always assume the player might fail at one of the puzzles and give them the ability to fix it somehow without having to go through the entire level to choose not to push the box
All in all, if you add some story to it and do some of these things I'm sure your game will feel even better.
Good job!