This is very promising. I like the mechanics, very interesting and fun. My only complaint would be that I found picking up and dropping blocks at certain angles a little finicky (for example, sometimes it seems like you have to position yourself just right at the edge of a block to pick up the block underneath diagonally to the player, that felt a bit weird, in my opinion). That being said, I adore the idea of a platformer where your way of gaining height is to stack up blocks, such a fun idea for a puzzle platformer! You have something great here, would love to see this expanded!