The story, first and foremost. I love that this game can touch my heart, in both happy and sad ways. After that, the people I play with, the art style, the fun jobs, and the variety male character models. (So sick of every game turning all the guys into "hulk smash!" muscle-bound he-men.)
Even if I run out of things I want to do in another year or so, I will have gotten way more than my money's worth and many of my best gaming experiences out of this game.