The Sims was the most phenomenally successful computer game of all time and the first relatively sophisticated social simulator for the PC. Its obvious gameplay faults have been torn apart -- by people experienced with simulations, and computer games in general -- in its node, but they ended up being irrellevant.
The overlooked key to The Sims's popularity among the non-simulation-savy was that it's a virtual pet game in which the pets are human-shaped: people read complex inner lives into the very simple AI models.
The sequel corrects most of the gameplay faults and rachets the realism up several notches. Maxis spent a fortune (and several years) making the characters' expressions and interactions realistic (and avoiding the uncanny valley), and now watching them tugs at your synapses. You can't help empathizing; your brain is hard-wired to empathize with things that act this human. Mostly, it's the cumulative effect of a hundred small touches, but the obvious improvements are
- Aging, from birth to death. Some aging is automatic; some is triggered by goal events (a first kiss, for example).
- Better graphics and greater visual differentiation between sims. If you have a lot of time on your hands, you can design a sim that looks exactly like you, down to the cheekbone shape and indy clothes.
- Memories and motives. The development team formalized and duct taped together several psychological theories to create the mathematical model governing sim behavior; sims will, for example, form associations between events, locations, and people (and can even develop phobias in some cases).
Realism aside, it's worth mentioning how big the Sims 2 conceptual space is. Its house-design tools are better than those in most dedicated house-design programs; there are a bunch of what are effectively minigames (aliens! ghosts!) to lure in people not much interested in the virtual social interaction.
The original spawned 7 expansion packs and dozens of free and fee-based (!) websites hosting additions. This game will be much bigger, and its effects will reach further into society at large. People will use it to plan (or reenact) their weddings. The first machine to pass the Turing test might be made by Electronic Arts. And brace yourself for an onlaught of CG porn in several years' time.