The Sims (I) was my favorite game by the time it was released. Together with a friend, we kept playing it for day and night... literally. We played it that often, that we (seriously) blew up the CD. I haven't played The Sims I since.
Sims II is quite a pleasant game, and I always had a thing for simulations, alas Football Manager and a few other similar type of games; nowadays I stick to the two usual games (Baldurs Gate and Football Manager). I'll probably uninstall the Sims II soon enough again though. It takes too much of my free disc space. The Sims II, Black & White, Diablo II and Anno 1602 are games I just feel like playing at a certain moment, but I usually don't keep them installed long. Anno 1602 is a different story though...
On a side note, when the Sims I was released, it was in general quite a popular game among just about everyone.
The girlfriend of my brother is a real addict to the game and quite a regular at the official site of the Sims.
The Sims II doesn't have much of a goal either, but it is a pleasant thought that age plays a role, so you don't redo everything over and over again. After a while, it does feel like you're repeating it, but that's usually the time I uninstall it. It still (just like the other four I earlier mentioned, Diablo having the least of it) has quite an addictive factor to it. I truly do adore the memory of blowing up my first CD though.
WoW isn't my type of game, regardless of what is said. I've mentioned that before.