Had a chance to play TS2 today for several hours. Very very impressive. The graphics are not the only improvement in the game, just the most obvious at first glance. The primary difference between the Sims and the Sims 2 is that many of the so called "needs" are more intelligently addressed by the Sims themself which frees up the player to address a new aspect of the game, "Wants". Wants are sort of like life aspirations. They vary from Sim to Sim and have much to do with which of 5 basic Sim types they fall into: Family, Fortune, Knowledge, Popularity, and Romance. Every Sim is one of those five types. Some career paths align more readily with some types of Sims, but no Sim is ever limited to what he can choose to become. That is up to you.
As a Sim grows older (and they will age from an infant all the way up to a Senior Citizen!), their aspirations/wants will change. More aspirations will appear when these are achieved. Some examples are: (for a Family Sim) Fall in love, get engaged, get married, have a baby, teach that baby to walk, have a grandchild. (for a Fortune Sim) Begin a career in Sports/Business/Criminal, Buy a painting worth X Simoleons, make 100 simoleans, gain a promotion, achieve top level in your career, own a mansion, etc.
These "desires" add a great deal to the game. Now the goal isn't simply to meet a Sim's needs so that he/she has more free time to play with, but to gain that free time so that you can help them meet their dreams. If you are successful in doing that, you will unlock new features, such as special items that make life easier or even improved longevity as an Elder Sim (retiree). On the converse, there are "Fears" as well, which act as the opposite of the "Wants". If you make a Sim realize his/her fears (which isn't as easy as you might think) you can turn them into bona fide basket cases and all sorts of strange behavior appear, including random acts of insanity and trips to the psychiatrist.
Numerous other improvements have been incorporated into the Sims 2. Added features abound from nearly every object that your Sims can interact with. Now, newspapers have 8 or more separate functions you can choose from instead of simply "look for job" or "read for enjoyment". And these new functions are Useful! For example, you can 'do crossword' which may increase your logic skill. Or "make airplane and play" which is a cheap way to address the fun and social needs. You can even "look for new home" which is a way for an adult Sim to strike out on their own, creating a new family unit. And that brings up another new feature: Family Trees. Sims will now remember their former relationships with Everyone they know. Family members, Friends, former lovers, enemies.. these are all tracked in the game.
Overall, the underlying themes to this game are experimentation and exploration. As the game designers said, they have not planned for every possibility and in fact, that was never their goal. They created a set of rules and then gave these to the players to work within or even "Break" as they wish, to explore the vagueries of human existence and relationships. The Sims will never be an accurate model of human reality of course, but as a fun diversion it succeeds with flying colors.
If there are any drawbacks to this game, they are minor: Getting used to the camera controls can take a little time, since they are reversed from many other popular 3D games. Sometimes it isn't always obvious what you need to do to complete a goal, and there is also some hidden information that you cannot readily gain access to (for example, when one of your Sims is sick, apart from them making frequent trips to the toilet, you would never know, nor would you realize how contagious they are.) Lastly, the system requirements are heavy. If you haven't upgraded your computer in the last year, you might want to do that before even picking up this game. I paid some visits to various forums and fansites and found the feedback overwhelmingly positive, but there are scattered complaints from folks who cannot run TS2 on their computer, or are only barely able to.
I give this game 9 full stars out of 10. Only the minor issues above kept me from rating it higher. Maxis has a true winner here, and a worthy successor to the greatest selling pc game of all time.
-Elgalad