Great game! And it is worth playing. As good as the first, but I hesitate to actually say "better".
Graphics
The graphics are of course supposed to be better, and it is better. The game has entirely turned into 3D, and the camera movement is more free.
Gameplay
Generally, the basics of the Sims series are not changed. You have to lead your Sims to good lives (or a bad one, if that is the intention), get a good job, get married, and get their moods maintained high. In Sims 2, there is another necessity; maintain a bar called the aspiration meter. The aspiration meter shows how much the Sim is satisfied with his or her life. The lower it is, the worse. By filling up certain wants and fears, you can keep the bar up or down.
In the sequel to the Sims, your Sims actually grow, age, and eventually die. However, hopefully you would've left some children by then, to continue on in your family tree. Some other additions are revamped animations, some interactiveness, and more detail. For example, you can see the people playing chess, making moves, and seeing the pieces.
Sound
The sound isn't really the most impressive factor of this game, but it is still decent. The Sims still talk their own language called Simlish, which is just mostly plain gibberish to the gamer's personal humor.
The Bad:
Slowdowns and bugs
This is not a completely stable game, and you can experience some freezes, glitches, and frequent slowdowns, especially on the highest game speed. My computer, which exceeds the recommended system requirements, still has some slowdowns in the highest game speed. Although I can understand that there are many things going on in the house, the slowdowns can be annoying.
Camera movement
The zoom in feature is great, but the others are not so as impressive. The scrolling and the rotation is awkward. Sometimes you scroll too fast or too slow, and combine that with the slowdowns and you get a camera nightmare.
Overall, this game is great. It managed to deliver the high expectations of the sequel. I think it's worth it, and you might enjoy it.