I'm a huge Tolkien fan and almost didn't buy this because I have a 4k system and there were so many negative reviews about picture quality. THEY ARE WRONG!
I'm running a 7.1.2 sound system with 4K video supported through a Sony VPL-VW295ES 4K projector, Sony UBP-X700 4k player, Denon AVR-X4700H 8K AV, and 21Gbps HDMI cables. It's stunning. Absolutely no audio or video issues. Given my experience, I can only assume that the negative reviews are coming from people who don't have the proper audio/visual/cable hardware to support Dolby ATMOS and Dolby VIDEO.
Never put LP records into your DVD player. Never put 8-tracks into your cassette player. Never go against a Sicilian when death is on the line. Never play 4k Dolby VIDEO discs in a system that doesn't support them.
And now a quick movie review: before buying the discs I had only seen the theatrical version. Just like with LofR, there is a HUGE difference. The extended versions are superior. You won't realize it until you see them, but 15 additional seconds here, an added scene there, 30 more seconds here, and suddenly this has all been tied together quite nicely with the books and the movies. There are in-jokes, riffs on subjects from other books, foreshadowing, etc., that was cut out of the theatrical releases.
Do yourself a favor - buy these disks, have the right hardware, watch the extended editions of LotR, and then watch the extended editions of the Hobbit (I know, the Hobbit occurred first, but it was filmed second so the subtle references only work in this direction).