Well, my controller is like 3 years old. So yeah, that left analog stick might be a little worn out. But as previously stated, this is the only game that gives me this kind of issue.
Concerning the D-Pad: I tried to play this with the D-Pad while regulating the character's walking speed with the Square button. But climbing with the D-Pad does not work for me because the stick appears to have a higher priority. That means that the tilted-up stick, as the game recognizes it, overrides the D-Pad's pressed Down-button. So instead of climbing down, the character slowly climbs up.
Usually I really appreciate rather sensitive and responsive controls in a game. But in this case, at least for me, the defaults don't work. And I don't see myself spending around €40 for a new controller just to be able to play this one game on the PS3 properly. It's a pity really, since I think I would really enjoy this game if it wasn't for this controls issue.
Regardless, I'm gonna pick up the Vita version of this game in the next few days and give that one a spin, too. Looking forward to it, since it will run on a brand new Vita console.