Although there are a multitude of rave reviews regarding the picture quality of this television set, actually achieving that goal is both frustrating and tedious. After unboxing and setup, don't expect to plug in the new TV, sit back, and enjoy your favorite programming as you will be sorely disappointed with the factory settings.
There are myriad "Expert" settings and combinations thereof with which the user can experiment in search of that satisfactory balance of color tone, brightness, sharpness, eliminating the "soap opera" effect, etc. Picture calibration (restricted to "Movie" picture mode) is even an option with the use of a mobil phone, but my experience with it proved to be less than satisfactory.
By all accounts, reviewers rave about the quality of the picture while streaming which may very well be accurate; however, there remains a large segment of the population who continue to subscribe to cable/satellite services. Therein lies the problem. Once you've managed to navigate the settings and achieve that perfect picture; change the channel/station and it all goes out the window. Nothing is consistent between broadcasting networks, programming, and even advertising; which only leads to more time wasted tinkering with the settings.
Viewing the spatter of 4K pictures and short videos in "Retail" or "Maintenance" mode provides an experience of unparalleled awe and wonder; a fantastic preview of the capabilities of this television. Unfortunately the translation is lost in "Home" mode.
In short, I have been a dedicated purchaser/user of Samsung televisions dating back to the early 90's and currently have two "older" LED sets, a 32" and a 49" (UN49NU8000); and though less technologically advanced, by all appearances they provide a better and more consistent picture with a lot less tweaking to achieve the consummate viewing experience than either the QN50QN90D or QN50QN90C . The older models have a "Natural" picture mode which has been eliminated in the newer models; unfortunate, as that mode seems to provide a good starting point to achieve a great picture with a lot less work.
One final observation: When entering the "Home" screen of the older models (now referred to as the "Smart Hub" in the new models), the current programming passing through the cable box/AVR continues to be displayed in the background which allows the user to exit and maintain the input source; even when exiting an app. Not so with these new models; though there is a "Live" option for live programming as a background, it lacks an ability/option to connect to the main source of input (ie: AVR). So, if an alternate input source is used such as an app, when exiting in an effort to return to the main source of input (again AVR), the user is forced to navigate to, and select/change the input source back to AVR, as it is no longer displayed in the "Recent" window; an added and aggravating extra step.
Overall, I give the QN50QN90D a grade of C; primarily due to my inability to achieve an acceptable, well balanced and consistent viewing experience across the entire spectrum of programming that our satellite network provides. To be clear, that programming is also available to us via fiber optics which offers no discernible difference in reception. In my humble opinion, for the current price of this unit, it should be blowing my socks off. In that respect, I'm disappointed because it doesn't.