Alright, first of all, going off of what Zenmetsu said, I loved both Super Meat Boy and Canabalt. Needless to say, I very much loved this game as well, especially since it didn't seem to have such a difficulty curve in it. However, having played only two worlds, I can definitely say that I was wrong about the difficulty curve, especially in levels that involve climbing or falling.
First of all, in a game called Mr. Runner, one would generally expect to be running most of the time. Levels where you ascend or descend are redundant for such a game.
Secondly, despite the smooth mechanics in most regards, there are one or two things which could use tweaking; for example, the rate at which you fall.
Thirdly and finally, the wall jumping mechanic is somewhat difficult to control. However, natural mechanics for any complex action in a game are almost impossible to come by, and I'm certainly no game developer. I suppose you aren't to blame for that problem,
Despite the numerous problems listed here, in no way do I wish to imply that this is a bad game; quite the opposite, in fact. It's addictive and quite fun.
All in all, good effort, and I definitely hope to see Mr. Runner again sometime soon.