No variable jump height, super fast movement speed, and immediate reversal of velocity in the air when trying to move in the opposite direction all combine to make for an awful controlling game.
Despite that, I really love the amount of work put into the game. And some exploits allow for sick vertical movement. Tree world and water world are both really good, however moving down does not work with the way the game plays. Lava world is a total mess (not that the others don't have their issues but lava world is definitely the buggiest).
Overall, it's fun (except for lava world) and It would be cool if the game were expanded upon.