The mechanics work very well, the rewards given by the climbing vendors entice the player into continuing, and the thought of "oh, I'm going to climb that mountain over there just because I want to" shows the effectiveness of the game's open world-type environment. 

However, the addition of dialog responses would help make the world feel more alive, as interactions with the inhabitants would be more dynamic. Also, this game would benefit from either a leaderboard or an online mode: comparing stamps with other players or racing them would be awesome! It would add competitiveness to the game and improve its replayability.

P.S. I like the traffic rocks. They force you to rely on timing and they demand calculation. Please keep them in the game.