The arguments over the Q9FN vs. Q90R picture quality are interesting, since I had a 65" Q9FN for about 6 months. When it failed, Samsung (after a couple of months of battling) decided to replace it with a Q90R. I was not able to compare them side by side, so my comments are based on memory of what the Q9FN was like.
Most of the discussion has been about the lower native contrast of the Q90R. I don't doubt the measurements, but question their importance to actual viewing. The lower contrast ratio is mostly caused by a slight increase in the light output when the output should be zero. I wonder if the human eye can even detect the difference. This is especially true when you consider that most viewing environments are not totally black. The reflections could completely mask the amount of light leaking through the LCD's. The blacks on the Q90R look at least as dark as I recall those on the Q9FN. Perhaps the new reflective coating on the Q90R reduces the reflected light enough to compensate for the lower native contrast.
Color reproduction seems to be a little better than I remember on the Q9FN. DSE on the Q9FN was only noticeable when I looked for it during a hockey game. On the Q90R, I can't see it at all.
Some have talked about dark blue edges. I never saw them in normal content. The other day, a very bright white image filled the screen. Those blue edges were visible, especially at the bottom of the screen. But, even though I know what to look for now, I don't see them in normal content, even hockey, with the white ice extending to the edge of the screen.
One thing that surprised me on the Q90R was the amount of overscan. I used the Digital Video Essentials HD Basics Blu-Ray, mainly to look at the gray ramps. The overscan pattern showed quite a bit of overscan. Changing Fit-to-Screen to On, reduced the overscan a lot. I have checked this with every source that I have, and if Fit-to-Screen is Off or Auto, then there is overscan.
For the record, I am using Rtings settings, except for the SDR backlight. I currently have it up a couple of notches from their setting, but am still trying to find a compromise that will work both with daylight and nighttime viewing.
Overall, I find that the Q90R gives a better viewing experience. We were happy with the Q9FN, until it failed, and are even more pleased with the Q90R.