Before HDMI became ubiquitous, every visit to my parents involved selecting the correct aspect ratio. It's clearly wrong, I'd despair. Oh, they'd say, really?
But yes, Blue Planet II and anything shot for UHD and not scaled or otherwise looks amazing. Everything else looks fine but there are artefacts and it shines a bright light on the production, but the colour depth and brightness of OLED is quite frankly literally amazing (we have an LG 65 inch monster).
By-the-by, watching the HD version of Wonder Woman the other evening, quite a lot of the VFX had the B5 quality.