For people with 1000+ hours on TS4 -- What keeps you playing?

Since the very beginning my focus has been on a goal-oriented do it all type of game play with mainly one family. I found out early on that when switching families I'd often wonder what was going on with the family I'd just left. Or I'd get ideas for a sim in a family I'd just switched from so I decided to just focus on one family and occasionally play one of the offspring once they grew up and moved out, just to get them settled in a new household. It keeps the game interesting for me because I rarely repeat careers, or aspirations, or leveling up the same skill for different sims. I'm just now getting around to running a vet business. Anyone looking at my family tree would see that I don't follow any type of traditional aging system in my game so I'm in no hurry to get things done.