I like it a lot! You got every aspect just right - really impressive.
The animated intro is an astonishing achievement, keeping the short time in mind (and also all the other drawings, that were made).
And the idea of zooming according to the speed *chefs kiss*
Regarding this last one, I have a suggestion: Instead of making the player hammering W after a collision, I would recommend to increase the speed automatically over time (doing it pretty fast would feel right, I think). Keeping the zoom-out, of cause. That way, the game would create a nice curve of rising difficulty and keeping the actual game play focussed to jumps and slashes. The higher the speed, the more points.
Hope you find this useful. Thanks for your entry - enjoyed playing it!