Awesome!
The concept of the game is totally awesome. The principle of using only one key really lets you concentrate on your timing. Its easy to learn and addictive at the same time.
The atmosphere of that abstract world, the worm that follows you, who never lets you rest one single second combined with the background music really makes this game f*cking awesome :D
One of the few games that still can make my adrenalin levels shoot up ;)