Very nice visual design and gameplay concept. Personally, it felt a little too difficult for a jam, and frustating when you've got your boxes to the perfect size, but then accidentally nudge them as you try to jump on. Perhaps giving a couple of extra boxes per level would help with this, meaning there are backups if things go a little wrong. Giving access to all levels really helped on this front though, and the whole concept definitely has legs as a full game. Really good stuff!