The Sims 3 is too complicated, the Sims is too simplistic, but the Sims 2 is just right! Getting the base game itself may be a bit hard to find, but I'd recommend the Sims 2 deluxe compared to more jam-packed versions with more expansion packs, because starting take would take forever, and then you couldn't download all the fun, free accessories online =)
It's hard to describe how a people simulation game where one makes families, houses, and controls the people can be fun. There is no end to the game, but trust, it's perfect for when you have a break, for example after finals week in university.