The Sims 1, 2, and 3 all rely on psychological addiction rather than promoting creativity and experimentation. Sure, there's a lot to do and stuff to explore, but once you start getting an idea of what there is to be seen, it gets boring. I found Vacations to be reasonably entertaining, but it all eventually came back to a nuclear power plant simulator: One thing needs attention, fix it. Next thing needs attention, fix it. Several things need attention, fix the most important and then the others. Ad infinitum.*
The only real fun that came from the game (For me) was playing it how it wasn't meant to be played: Screwing around and killing people, which I can do in most other games with a great deal more enjoyment.
It's a sandbox of the worst sort - One with thousands of useless tasks you have to repeatedly do while working towards a hazy, not-so-satisfying goal. Once you finish that goal, there's only vague tasks to follow beyond that, and none of those include the sheer thrill of survival (Unless you intentionally or accidentally mess something up). Just point and click. The problem multiplies itself as you add more household members.
That said, when I start playing it, I just can't stop.
Not the game for everyone, certainly, and certainly not something I'd recommend paying full price for, unless you're really into a semi-humorous real life simulator, boring bits included.
*I guess it wouldn't be a bad way to keep nuclear plant workers entertained, though. Homer Simpson might actually (seem to) know what he's doing!