Well TS2 had a layer of realism that TS4 does not have.
Animated cars, having to shop for clothes and groceries, interests, long time and short time relationships, fears much better wants, the aspiration meter that gives the player the bigger goal right from the bat, etc. It really did put an emphasis on the actual sims and how they socialize and live. The fact that you can also have custom worlds in TS2 with an integrated create a world is butter on top. It was just well crafted.
TS4 just doesn't have that, it has a different focus. In 4 years the sims themselves have not changed or have been added anything to. The realism gameplay that it lack will never be changed at this point in it's life I don't think so it's not as detailed in what comes to being a life sim.
