It's better because it's not Sims 3. :p :D (No shade to those who like it, I just... didn't.)
Vampires are most definitely better than ever.
Toddlers are the best because I actually want to play with them sometimes.
The worlds are gorgeous and feel more "filled in" and immersive. I really love this art style.
CAS, as far as physically creating a Sim, gets top marks. I'm not one who feels the need for a color wheel and since they've been adding more basic black and white and neutral swatches, I'm very happy with it. I can actually create likenesses of real people and fictional characters alike without any CC, and a variety of body types too. And something I've wanted since Sims 2 is unisex CAS, which they delivered.
The Gallery is one of my favorite things because I love getting builds from there and being able to upload all my Sims to declutter my Library.
The weather effects are amazing (despite snow having no depth.) The blizzards, the thunderstorms, and the variety of climates in each world is something completely new and adds to environmental immersion.
Some beautiful animations exist in this game that definitely rival previous games. I wish there were more, though.
The ability to travel between worlds is absolutely one of my favorite things about Sims 4. There's a freedom and variety in it and it really makes the Sim universe feel larger and more diverse.
And, of course, the diversity itself. Actually having curly hairs and a healthy selection of cultural choices and varieties in not only CAS, but some of the build/buy as well... really bumps this game up a notch for possibilities.
Finally... I'm just going to say it. First person camera. Oh yes, I'm serious. It's another thing I've wanted since Sims 2 and it makes me happy.
