I love CAS and being able to chose 5 different outfits for each category. I only choose one outfit for sleepwear and swimming and use the remaining slots for additional everyday wear.
The Gallery. I'm not a builder so I do love being able to download lots and rooms directly into the game.
I love that I can travel between worlds to visit family and friends. Because of this I'm not feeling the need to have all of my community lots in one world. I can send my sims to Sulani for a day of fun and sun on the beach and the next day they can trek the jungle in Selvadorada.
I like the emotions. I like trying to get my sims into a particular emotional state in order to complete a goal. Write a book, paint a masterpiece, school performance, etc.
Gardening, evolving, and grafting.
Toddlers. No need to say more.
I love the goal based aspirations, careers, and events.
I love that my sim can complete multiple aspirations.
Love the fame perks and quirks, and vampire ranks and powers.
Love the introduction of character values in Parenthood.
This list is hardly exhaustive but just a few of my favorite game play features off the top of my head.