How about we get some Sims that aren't all dolled-up with CC for a fair comparison?
he says, having custom sliders
http://i.gyazo.com/35930052872382b82f6f5c6046fc4e67.png
I have to say the only real difference, aside from style, is that the Sims in the Sims 3 have much 'softer' features around their face, things are rounder, while in the Sims 4 it's sharper. However, you can work around the soft features if you try hard enough.
http://i.gyazo.com/3329acf3a45eb5f5ff0133f226d009be.png
The other big thing that makes Sims 4 Sims much different and much sharper is the fact that we have presets to work with - Preset jaws, lips, eyes, cheeks, and brows. In the sims 3, we're all given the same shape to work with and mold to our liking, and while we can make people look really different with it, everybody will still have the same nose, or the same lips, or the same eyes, just morphed into something else.
Sims 4 does have the better CAS, but it falls short of everything else. Give me open world, recipes, and CASt and then it'd be a really great game. Just give the sims 3 multitasking and it'd be what the Sims 4 should have been.