After using two years the D800e i used the d810 now for one week.
Most of the changes refer to handling and being able to get the shot and control the details.
group AF is very fast ; very silent shutter ( at last!); 100% good quality liveview
split liveview - so you can see the depth of field / sharpness at different points. very useful.
bracketing is now possible with two and three stops difference - a highlight priority matrix meter. Electronic first curtain
The resolution is about the same. the image has improved but only slightly… you need the best lenses to see the difference.
The details are more precise ; as other pointed out ; the image looks a bit more 3d.
The files have more contrast; i used for the d800e the standard camera profile in ACR and now i use the Neutral ( softer profile)
I need slightly less sharpening on the d810
As some pointed out ; some lenses seem to have more depth of field. ( the 85mm 1.4G for one)
The colors are different- more pronounced as if a slight cast has lifted.
Looking at all the digital camera i have used through the years it is another step forward in making the image look more photographic and less graphic.
I have been trying to put words around this, and you have it well described. It's the cast issue that I always saw with the D800 Family. It could be corrected in post, but it was strange, the D810 sure has a better base WB control.
After shooting both cameras side by side now in many night long exposures, no doubt the D810 is the winner, overall much cleaner in all aspects, from base iso of 64 to 3200. The 810 without the white dot fix was a MESS, but after getting the fix from Nikon it's very clean.
This also confirms my suspicion that early models of the D800e had this same issue. Nikon fixed this behind the covers on later cameras. I noted this from day one with my D800e and wrote about on my blog many times, and attempted to get Nikon to replace/fix the camera. When I saw the comparisons of the early D810's to D800e's the D800e's were very clean, so I knew Nikon had made a fix. Same fix apparently that was let off of the D810 at first. I have used 2 other D800e's in workshops I have conducted all in longer exposures and both were free of the white dots. that mine has.
Live view is the other huge improvement over the D800 family. You now can still focus in low light without way too much noise. There is some noise, but nothing like the D800e has. The review screen of the D810 has the green bar to let you know where 100% view is, ( a great help). and you now have the EFC option.
Well worth the upgrade.
Paul