Very interesting and fun concept. As others have said, a lot could be added and refined but its a really great start to this idea. I really love the idea of "drawing the level".
Excellent concept, but it's a bit buggy. I've like to see this worked on some more. What if you could get an eraser powerup so that you didn't have to clear everything if one little part has ink in the wrong spot? What if you had a limitied ink supply, and hand to collect more? The physics needs a bit of work. There was a level where I kept dying for going too far to the left, even though there was no spike and the wall was still a goo 30 pixels away.
Very interesting concept, but it's got some bugs/exploits. For example, you can just draw a "pillar" under yourself to go straight up. And I think the slope of hills you can climb makes it very easy. And you can fall through floors. And the collision detection seems a little off (I didn't touch that spike!) Just needs some polish.
Buggy, innovative, shows potential.
Give us Version 2.0!!!!