Very nice! its a fun little game and fits the theme perfectly! I do have to say that i don't like the controls, the don't always respond well and i get confused non stop what direction button i need to press. Not sure what would work better, but this is not it.
Also the tutorial was (for me) not super clear that i had to push the crate to move the crystal. Maybe i missed something but i was trying to move the crystal without the box and got a bit confused. I really had to figure it out so maybe making it more clear with the box that starts flashing so i know that i need to move it? After this i love the mechanic and it was harder then i tought just moving a box and thinking ahead. But it really was a lot of fun!
I would also say the game could do with a bit more visuals, maybe a moving background, some partial effects. but that's not really game-jam stuff but it felt a bit empty sometimes. But its understandable :D but still i really liked it!