It was a lot of fun climbing to the top and finding my own way through it. I like how freeform the level design was. It gives the opportunity to pick your own path and change it if you can't figure out how to get past a certain obstacle. It was a very good idea to make the ledge-climb mechanic so generous, since platforming in a 3D game can often feel clunky, especially when the platforms are physics objects.
Controls for switching box and resizing modes felt a bit clunky. think having (different) sound effects for switching would have helped a lot. The cooldown for item pickups also felt a bit pointless. Why put them on a timer if I can just sit there and collect the same object until my inventory is full? Small nitpicks though. Great job!