I like the art style, for both sims and the worlds. I wouldn't want my sims to look like real people. By which I mean, I don't want them to look like I'm watching a real movie. The semi-cartoony style we have now is perfect.
The CAS is fantastic. I can do so much more to create a unique look than we could do in Sims 1 & 2.
The worlds. Some of them are breathtakingly beautiful. I like that we have a variety of worlds to choose from.
Seasons is - well... The change of seasons add a lot of beauty, but I'm still getting used to it.
Little things make it so fun. I like flirty animations, gloomy sims moping around, and cheerful sims.
Knitting pack. One of my favorite packs, this one is a must have. Not only is Plopsy great for sales, the knitting animations are darling. I really love watching one sim teach another sim to knit. The hesitancy of the new knitter, their body language and expressions as they show their work, and the encouraging nods of the teacher - I never tire of watching. I just want to give them both hugs.
Vampires - I like that they have so many steps and so many ways to have each one unique. I like that we have different fangs, facial markings, etc.
It is so much easier to build in Sims 4, and we have a lot of ways to build and styles to choose, even for those of us who play vanilla.
The Gallery. I can download a sim or a build and make any changes I want to make it my own. This is so helpful, especially for build styles I am not familiar with.
Sandbox. Oh, please, never take away my sandbox! I must be able to build and play according to my own taste.
This game can be such a boost to my imagination. I love it for that, most of all.