Good concept
The concept was great (though it's pretty much Draw-Play without the flags.. or obstacles...) but you need to work on it more. Having the restart button invisible made it hard to find at first (I actually found it by accident doing that "raise the player" trick). Also, having it in the middle meant it kept getting in the way. I'd go to click and it would restart.
Also, it should have a clear button to clear away all that you've drawn. And along those lines an eraser.
Another review already covered colours and line sizes.
Anyway great "sandbox" concept, it'd be fun to play around with (just like linerider), but it needs a LOT of work to be one of the greats. :)