I can't vouch for Blue Planet II, and Planet Earth II is outstanding, but during episodes the film resolution sometimes changes. Of course, due to the source material, but it's not 100% eye love the whole time.
In my opinion, of the discs I've seen, these would be my picks to really showcase 4K UHD and Atmos/DTS:X. I give bonus points to titles in Dolby Vision.
- Atomic Blonde
I love this movie in its own right and enjoy every repeat viewing like it was the first. The movies uses color to great effect contrasted against a dreary 1989 Germany, all in Dolby Vision. Its DTS:X surround track is a great showcase that Atmos isn't the only game in town. The sound stage gives space and breadth to the amazing music soundtrack and the action is as ferocious as Lorraine. This movie does come from a 2K DI.
- Blade Runner
Seeing Blade Runner this way is damned near the second coming of Christ. The filmic clarity 4K offers so much detail and the futuristic world Deckard lives in is displayed with such an outstanding HDR10 mastering. Nothing is lost in the dark scenes and upper end of the contrast spectrum is marvelously displayed in the city lights, neons, and colorful displays. To say nothing of its Atmos track would be criminal. This is the Atmos track to showcase (though see my next entry). Overhead channels are used to fill space, but also excellently implemented to bring the viewer into the scene.
- Blade Runner 2049
Seeing Blade Runner 2049 this way is damned near the second coming of Christ. The filmic clarity 4K offers so much detail and the futuristic world K lives in is displayed with such an outstanding HDR10 mastering. Nothing is lost in the dark scenes and upper end of the contrast spectrum is marvelously displayed in the city lights, neons, and colorful displays. To say nothing of its Atmos track would be criminal. This is the Atmos track to showcase. Overhead channels are used to fill space, but also excellently implemented to bring the viewer into the scene. The soundtrack is integral to this movie (also see: Atomic Blonde) and I simply can't imagine hearing it any other way. Not to overuse the faith-based metaphors, but each of my repeat viewings (oh, and there will be more) are practically a religious experience for me.
- The Fifth Element
A true showcase of 4K bringing film to our screens without compromise. The HDR10 mastering really brings forth the brighter elements of the film (Leeloo's hair, the Opera scene, etc.). It's not an overly dark film, but details are never lost in the lower end of the spectrum, either. The Atmos track is superb. The action scenes are great showcases, as debris, bullets, and flying cars surround the viewer in all axes and sound graciously fills the room. And, of course, the Opera scene is just breathtaking rendered in Dolby Atmos.
- IT
Another 2K DI, but the Dolby Vision mastering of the film, whether it's the color seemingly drawn from Pennywise's home, the dark sewers, or the bright shades of Penneywise's makeup, they are all rendered clearly. Yet this movie does not exist on my list for picture quality, as there are much better uses of HDR elsewhere, but, rather, for the Dolby Atmos mix. Literally from the moment the movie opens the additional overhead channels are used excellently and there are many more scenes throughout the film that exhibits the same philosophy, using the entirety of the space to a nearly fun house effect.
- The Matrix
Anyone that saw The Matrix when it first came out will likely utter a similar sentiment, but I walked out of the theater changed. So, what other movie to showcase the great technological changes this new format brings? Coming from a true 4K scan of the film and mastered in HDR by the Director of Photography, Bill Pope, I don't know how I've watched this movie throughout the years in any other format. The Dolby Vision contrast is outstanding, with gracefully reproduced tones, but it is the darker elements of The Matrix that are the true showcase. The blacks are black and all the darker scenes have an outstanding depth to them, allowing nothing to be lost in the various contrasts of the scenes. The Dolby Atmos track is not of the funhouse variety that It is, but its each element in the scene that is heard distinctly, clearly, and with oomph. Bullets, cracking wood or concrete, a haunting quiet as the Nebuchadnezzar is powered down, or a minigun all have never been heard like this. The Lobby scene was always a great surround sound showcase and it carries that title with it into Dolby Atmos.
- Pacific Rim
I got too passionate about this post and it's time for bed, so I'm gonna cop out on these last two. A beautiful picture with excellent use of HDR10 and a Dolby Atmos soundtrack that outstanding, both in its channel usage, but also in its range. High squeals, thunderous roars, and everything in between highlights what Atmos can do.
- Saving Private Ryan
Dolby Vision, war scenes rendered in exquisite detail and channel usage in Atmos, and a gorgeous reproduction of film transferred to 4K.