This game certainly has a lot of potential.
I enjoyed playing this game and I believe more could have been done to make it stand out from the rest of the games that share this same concept.
First of all, I think including a soundtrack that captures the sense of terrifying speed would greatly improve the immersion.
Second, a little animation of the the horse getting crushed between the edge of the screen a cliff when you can't make a jump in time would add to the overall experience.
I do like the fact that each run is random and there are some runs where you are luckier with the cliff placement than other runs. However, a level designer would also be nice to add more interactivity.
I really liked the scoreboard because it introduces to the player a sense of competition to see how his score compares with others.