I have noticed one thing that is important to me. The turbulence seems to be improved.

It is a completely subjective thing, but I never got the turbulence to feel realistic in G3/G3.5 and I tested that a fair amount. With my newly installed G4, I tried setting it, thinking, "here we go again", and darned if the first setting gave pretty obvious results. And it seemed realistic to me. I've since changed it a bit to see how it works over the range of values, and it continues to feel real. I'm pleased. And not entirely sure it wasn't just me. But you know, subjective things are like that.