Check out Unlocking the Psychology of Achievements, via GameCyte.
I have an in/off relationship with Achievements; I love it when games use Achievements to highlight interesting gameplay native to the game, and I think they’re an interesting tool for creative teams.
But this part depresses me:
Based on personal experience, completionists need goals to achieve and do not enjoy open-ended game experiences.
In a way, it feels like Achievements cater to some inner obsessive-compulsive, rather than encouraging play in what I see as the right spirit. Is the player there to immerse himself in the experience or to carefully set up a situation where he can get three enemies in a straight line and headshot them all with one bullet?
Given the nature of our medium, I suppose both are actually valid in their own way.