Sims 3 (with Pets Expansion) is a truly immersive game. My daughter (who is 11) loves this game so we had it around the house. I decided to sit down at her computer and give it a spin. I have played Sims before, but not since the original version that was released around 2001. Sims 3 is much more involved and seems to be the equivalent of an MMO to the original's single player missions. The first huge change I noticed was that I can go all over the place. The original game was based around life inside of your house. This version, though, allows you to go downtown to the library for a book, a diner to eat, and so on. I was pretty amazed by everything that is going on in the city with the NPCs I watched.
Another big difference was the job. If I remember correctly, in the original version it just showed you leaving for work and you would basically stare at your house until you came home (which could be sped up by increasing the rate of time). In Sims 3, you actually get to go to work. Since I was a fireman with my new character, this involved riding on the fire truck and hanging out in the firehouse (which even had a fire pole).
I can definitely see why my daughter likes this game. I had only planned to play for an hour or so because I wanted to finish this review, but ended up playing all night. The open aspect of the game has definite replayability, as the player can choose many different paths for their character. Sims 3 is a great game and is worthy of its lofty sales numbers.