The appearance of the User Interface (UI) is excellent, and cannot be faulted.
However, the functionality of the UI is severely flawed. If you purchase the ATV hoping to take advantage of an HDR or Dolby Vision (DV) UI with screensavers in beautiful HDR, then PLEASE BE WARNED!
If you set the ATV video output to 4K HDR or 4K DV, the ATV UI is not actually designed in that format, and nor are most of the applications (eg Apple movies, Netflix, Apple Music, Tidal). So the ATV actually modifies its own UI (sounds bizarre, right!), to convert it from SDR, into HDR or DV. Unfortunately, THIS DOES NOT WORK properly. Using those settings, the screen will go black and audio will stop, for a few seconds, repeatedly, while trying to watch a movie or tv show, or listen to music. This essentially makes the ATV UNUSABLE!
The ONLY workaround is to set the ATV video output to 4K SDR, and to "Match Dynamic Range - On" and "Match Frame Rate - On". This fixes the audio and video playback, but you lose the benefit of the ATV UI and screensavers appearing in beautiful HDR. Please Google this issue before buying and you will see it has existed for at least 3 years (across both the 1st and 2nd gen 4k ATVs), yet Apple has done nothing to rectify!
Other significant limitations:
- Audio output is downsampled to a maximum sampling rate of only 48kHz! This means you CANNOT output 24-bit/192kHz audio via HDMI, even if you pay for Apple Music Lossless or Tidal HiFi Plus (and even though HDMI 1.4 and earlier can support 8 channels of 24-bit/192kHz audio).
- you think you are buying for HDMI 2.1, but the ATV CANNOT output 4K120Hz or 8K60Hz! Although this issue is less important as limited content is available on those formats.
Tested on Sony OLED A90J and Marantz SR6015 AV receiver.