There are quite a lot of running games around (here’s a list), but the one that really stands out is Run 3.
It is made by Joseph Cloutier and Alex Ostroff. Even though Run and Run 2 were good already, Run 3 takes the game and genre to a whole other level.
It has everything: simple concept, fun graphics, and most importantly: the difficulty level is just right. The player constantly gets the feeling: “I almost made that!”. Anyways, the game is tons of fun, and people all over the world are playing it. You should too.