I really enjoyed this game! The atmosphere and the visuals are fantastic. Loved the little detail where the small character had the key on his back, if you had one. The music and sound design was perfect, the music was gentle but mysterious and the sound effects were subtle, it created the feeling of exploring somewhere abandoned but full of secrets. The puzzle design was good, not too difficult but still engaging, I played the game all the way through to the end.
The only place I really got stuck was very early on, in the room in the screenshot below. I feel that the door itself is a bit misleading, I saw the lock on it, but it also looks like there's a hole in it where the small version could fit through (the little black spot in the bottom left). It made me think the lock was a distraction and getting the little guy onto the platform was the goal of the room, but I couldn't figure out how to do that. Eventually I did figure it out when I finally saw the "key not found" text at the top.
As others have said, the camera could be a bit difficult. Personally, the mouse click to rotate felt odd to me, and it took a while to get used to. I feel that maybe Q/E for camera and mouse for interact may have been more intuitive, but that may just be me. It also felt way too zoomed in when I was in the smaller form. Also, the ice physics on the movable blocks was a bit difficult to work with.
Overall though, really great game for a four day game jam, I had a lot of fun playing it!