The Sims 2 differs in that it's totally in 3D. The first sims series was only 2D... plus now there are actual goals for your sims to meet. They have life long dreams and aspirations, they basically tell you what they want now. Also, you're sims have a lifespan. Sims actually grow from infancy to kid, to teenager, to adult to elderly over a period of time. You have to meet your lifetime goals before they die. Not to mention Genetics... genetics pass down from generation to generation. It's interesting.
Jennifer