It works well, the platforming feels right and fair. The core gameplay is solid.
Now besides the obvious lack of music and sound, the game mostly needs 1/at least one thing to spice up the gameplay (moving blocks, ennemies pushing you, time limit, etc) and 2/ some animations or UI elements to add to the game feel; the square could squish a little when jumping, the timer to be a lot more prevalent, etc.
As a prototype it does it work, but as you probably know it needs a bit more to be engaging.