Multiplayer + Many levels for single player mode
If you just make it multiplayer ( like the del button makes the other guy run) it would be a simple cool game for 2 players. Or more if you like.
And for the single player mode you can put level after level the enemy to be faster.
Overall i liked the game and the 6 is so that i can put a better score for the second part the " Run till your fingers bleed" multiplayer version
Good job