Kaido, don't mash up PQ and pixel density. You know darn well the two are not related.
I have excellent vision but like others have said, unless you're up close to the set it's a total waste at that size.
Disagree. I've put in nearly two dozen 4K UHD televisions this year, including budget Sceptre, Seiki, and Insigina models (including a 43" Best Buy model in my own home), and have yet to find a brand that looks like crap. Whereas I've seen plenty of 1080p sets, particularly the cheapie models, that look absolutely horrible...muddy blacks, bad colors, etc. Maybe they exist, I don't know. All I know is that out of the literally dozens of 4K TV's I've installed, they all have pretty great PQ thanks to the extra pixels, no matter the brand name.
That doesn't mean that every 4K TV out there has eye-popping picture quality. The best TV I've seen so for is the 75" Sony X940D with HDR...but hardly any 4K sets stack up to that level of PQ (in fact, I didn't even like a lot of the other HDR-enabled sets I saw). My point is that the extra pixels in 4K televisions give even budget brands an image quality boost; basically, you can buy a cheap 4K TV & not get a complete pile of garbage, like you might if you got a low-end 1080p set.