Lovely little game and nice concept. The sound fits the mood perfectly. As your character turns happy to sad perhaps add a different music track for unhappy vs happy. I like the checkpoints as I died A LOT. I did get stuck in the blocks from time to time, perhaps add a mechanic that pushed the player up to the top of the block if it reappears when the player is in the way.
I prefer to use WASD to move which made controlling the character more difficult.
Overall I enjoyed it, I played it through a few times but I couldn't reach the end of the level.