The JU6400 is the entry point of Samsung's 4k TVs. It doesn't look cheap, has very little blur on movement, and delivers excellent performance for video games. Unfortunately, the picture quality in a dim room is bad (blacks will appear gray), and judder is present on 24p movies.
The JU6400 is a mixed bag. It is an excellent option for gaming, great for sports and well-suited for a well-lit family room. Unfortunately, it won't be as good for movie lovers who like to watch TV in a dim room, as the TV has poor blacks and suffers from judder. Depending on your viewing habits it can be great, or bad.
The 55" Samsung UN55JU6400 that we reviewed has a PLS panel (version FD05), which is a sub-category of the IPS family, and which produces grayish blacks, and has a wide viewing angle. If someone comes across a different type of panel used, let us know and we will update our review. Thank you in advance.
Some of our visitors reported that the 40", 43" and 48" version of the JU6400 has VA panels with better contrast ratios and worse viewing angles.
Contrast is really poor on the 55" UN55JU6400, and blacks will often appear gray. Those flaws won't be too apparent in a well-lit room. Other sizes of the JU6400 doesn't have this problem.
Like other IPS TVs, the 55" one has a wide viewing angle. Colors remain saturated at an angle, though the picture darkens a bit. Other sizes of the series have worse viewing angle.
Update 01/06/2017: We have changed the methodology of testing. Since this is an old TV which we don't have anymore, we extrapolated the results from 2016 TVs.
Judder in movies isn't too noticeable, but this TV cannot eliminate it without the use of the soap opera effect ('Auto Motion Plus').
The very low input lag is among the best you can find when you set the TV to game mode. In PC mode, the input lag is still good, at 34.9 ms.
Unlike other 4k Samsung TVs, the JU6400 doesn't do 4k @ 60Hz @ 4:4:4 (there is no 'UHD Color' option). To get Chroma 4:4:4 in the other modes, label the input as 'PC'.
There isn't a huge variety of apps, but the Tizen OS feels intuitive. The basic remote makes navigating the smart features less pleasant, but it is useful enough for navigating all the TV settings.