I had a chance to spend some quality time with my 75F6400 this weekend (rare weekend when the wife and kids were out of town). I used Buzz's settings from the F8000 thread as my starting point. After watching a couple of 3D blu-rays, a couple of 2D blu-rays, and several football games, here are my thoughts:
-3D picture quality continues to impress me. I see no flickering, no crosstalk, no artifacts. Looks better than any passive 3D setup I've seen (theater or otherwise).
-Black levels are surprisingly good for an LCD TV. The black bars during movies blend seamlessly with the black bezel, and shadow detail is decent.
-I love the size of the TV. I finally feel immersed in the material, which was my main reason for upgrading from 65".
-Off-angle viewing is horrendous. My primary viewing position is maybe 10 degrees off-angle (can't really fix this due to layout of the room), and even at that slight angle there is some (albeit minor) picture degradation. Anything beyond 20 degrees is pretty much unwatchable. Coming from plasma, I knew this would be an issue but I wasn't expecting it to be this bad. Is it due to the particular type of panel that Samsung uses?
-Auto Motion Plus is useless (to me). The recommended setting from the F8000 thread was 10 motion/5 judder. With this setting, I saw heaping doses of SOE and lip sync issues in 2D blu rays. For football games, the ball would disappear mid-flight. I turned off AMP, and all of these issues went away. It looks like people have had success with the "Clear" setting as well.
-Clouding. The clouding is much less severe than when I first fired up the TV, but it is still there. I think it's somewhat related to the poor off-angle viewing, since I will see clouding primarily on the left side of the screen if I am slightly off-angle to the right, and vice versa when sitting to the left.
Out of those, the only one that really bothers me is the off-angle viewing (any tips to mitigate this issue?). I knew that going from plasma to edge-lit LED would involve tradeoffs/compromises, and overall I'm happy with the TV so far.
The bottom line is that when I slip on the ridiculous-looking 3D glasses, dim the lights, and crank up my Klipsch speakers, I truly feel like I have a theater-quality experience at home. And that's really what it's all about in the end.