I haven't played any Sims games in a very long time (mostly due to lack of time, since these games always eat up the hours like crazy), but I am a huge fan of the series. Sims 1&2 were absolutely brilliant games, and I got my fair share of enjoyment out of the third one as well.
I must admit that I haven't played the fourth one yet. The lack of time is one factor, but I've also been meaning to wait until a few more expansions have come out.