Thank you guys very much!
@Damocles: Hehe, watch the walkthrough if you still have motivation left to test it.

I've uploaded a slightly different demo: some small bug fixes, the wallrun-walls are brighter, there is a timer and a counter for collected milk bottles now.

http://www.superku.de/Demo1b.zip
(password: iamtheone)

You can play the demo with a gamepad, too, just plug it in before you start the game. To change the screen resolution you currently have to open "data\slots.ini" and change 10 your desired mode.

If you did not finish the demo because something (/the game) sucked or you got stuck, please report it here!