They make you want to buy the Xbox 360 version of the game, if it's multli platform. Just knowing that you get more out of the 360 version and the other version are lacking it, it make you think the other version are gimped somehow.
For some reason when I play a game without achievements now, it feels like I'm wasting my time. Nobody is going to know what I did and I get nothing in return.
I'm not really that heavy on getting the achievements, but just knowing that they are there makes me feel ok with playing it. It's like the game gives me some love back after I spend some time with it. Without achievements it's like you date a girl and keep on getting her stuff, but she never gives you anything back in return.
I do like to peak at all my friends achievements and try to 1up them, just to make myself think I'm better than they are.
I know there are a lot of games that I have that I want to beat without achievements, but those end up being put on the back burner.
