'Challenging' it was allright. Challenging as in: I couldn't make it past the first two fireballs because of the floaty controls. I think I tried for 10 minutes jumping on the two rocks to get over them until I gave up. Sometimes I just got stuck in the rocks themselves. Other than that I think the pacing was acceptable to get some fun out of it. I like the stick figure's running animation. The graphics were nice, even tough the floating rocks look like pixel art, which doesn't really feel in sync with the rest of the visuals. The music you added was certainly a good choice tough :)
All in all tough, a very basic runner that isn't all that much fun. At least for me.