Jill Johnson (SimGuruJill) showed us the the most important chances and then we got to try CAS on the computer ourselves.
The new CAS looks very lean and with only a few controls which gives you a bit of a scare at first. The biggest change is that there are (hardly) any sliders anymore. Everything is manipulated directly on the Sim itself.
You can see how that works in the official Sims 4 gameplay video