Easy to mod - Didn't mod 1 or 2, but 3 was kind of a pain to mod.
The Gallery - Not much of a builder so I love being able to download other talented simmer's builds
The fact that sims look at each other - Sims actually follow other sims with their eyes even when not directly interacting with them, which feels more natural.
Sims continuing conversations after I initialize them - I like I can start a conversation and they'll continue it on their own without needing me to micro manage them.
Supernaturals having two forms - It's nice that unless you interact with a supernatural, you can't really tell they are one (except ghosts), allowing us to more easily ignore them in certain saves.
The fact that the base game is still being expanded - The base game we have now is way bigger and better than what we started with, and it will keep expanding and improving through free updates.
The variety of work options - We have follow your sim to work, work from home, freelancing, odd jobs, part time jobs, and registering for whatever job you can come up with.
Being able to jump from one world to another - Loading screens don't bother me and I like the variety of places I can take my sims.