The one downfall both Sims 2 and 3 had is that the time moves too quickly, so you have little free time to do anything with your sims except to make sure they're fed, make sure their hygiene is good, and get them to work.
I knew of the series from before when it was hugely popular, but right before the third came out, I said "forget it, I'm going to buy it and try from the start what all of the fuss is". I tried the first and loved it, but didn't see the appeal of spending 24/7 of my time, and all of the money, on a base game a million expansions and such. I jumped on the third when it came out (and got a special deal on the second a few days before to get me up to speed on the formula), and I have loved it since. I now own every expansion and stuff pack, and some store content. It does add up to be expensive for casual users, so it's a bit tough to recommend it all, but you don't HAVE to be a mindless obsessive girl to like the game, and you don't HAVE to buy all of the extras.
The base game could be found on sale here and there (was recently on Steam). It's worth the ~$20 when it is for just the base game. The expansion packs add SO much more, but are admittedly not as offering for the value as the base game is (especially since it's dropped in price). Thousands of people buying up all of The Sims stuff means EA overprices it.