I don't own a game or gaming system that has any type of achievement system, but imo, I think that a game should be good enough to make you to want to explore the world more and that will reward you with cool little doodads or something that open up other areas of the game for more exploring. Imo, a game or system that gives you little achievements sounds a little weak, unless you can get any game you'd like after collecting so many achievements or something as the only games that I ever played that really made me want explore more is The Legend of Zelda: Orciana of Time and Morrowind: Elder Scrolls IV or which ever one came before Oblivion.