It's a good start. I was able to run beyond the screen, resulting in the game eventually stopping. Having to constantly stop running in a run game to make sure that you're at a comfortable difficulty or to keep from going off the screen is pretty annoying. It would make sense to give a fixed running motion and allow the player to move left and right, or--should you choose to keep it with the player having full control of the running--allow the player to run to the left as well instead of waiting for the screen to catch up. Another alternative is to have a fixed running point and left/right controls the speed at which the game runs.