I was obsessed with the first Sims and have spent a fair amount of time on Sims 2 as well, but I never really got into Sims 3. I have all of the expansions that I wanted for Sims 2 and have been satisfied with replaying that one.
There are many different kinds of Sims players, and the problem for me is that the newer games are trending away from my purpose for playing. I enjoy the "boring" day to day stuff that we have to make them do, like eating, going to the bathroom, getting to work on time, studying, etc. I couldn't care less about going out on the town or shopping or visiting neighbors. I want to spend hours and hours meticulously building and decorating a house and creating Sims, and then spend hours and hours meticulously controlling their lives. For instance I would never leave the Free Will box checked, that would defeat the whole purpose of the game to me.
It became clear to me that this was not the typical way to play, and not the direction that the series was going in, when I participated in a focus group for a new Sims game a few years ago (Sims Castaway, I think it ended up being called). We all got to play the new game and then give our feedback in a group setting, and I was clearly the odd man out. I started with, "It's completely ridiculous that they only go to the bathroom once every two days, that's not realistic at all, and why don't they need to eat hardly anything? Too many directed tasks are given, I would prefer to decide on my own everything they do." The rest of the group looked at me like I was crazy and said that was their favorite part of the new game, not having to focus on daily tasks.
And so I think I'll just stick with Sims 2, which is really the perfect game to me.