[noggin]

Now, the bad:

• HDR10 content has raised black levels
  

If that happens in Netflix, I suspect Netflix will tackle Google pretty quickly. Does it do it with Dolby Vision content in Netflix too? If so Dolby may well have words as well - as their licensing probably requires decent quality output.

• No automatic refresh rate switching
  
• Refresh rate app does not work
  
• No automatic refresh rate toggle in settings
  

I'm not surprised about the frame rate issues.  It seems no Android or Android TV solution currently supports fully automatic refresh rate switching (without the app having to implement it, but instead the OS handling it automatically based on the frame rate of the video being played). The nVidia Shield TV has a kludge solution where their OS/firmware allows you to manually sample the frame rate of video once it has started playing, and Android TV on the Shield TV also implements an app controlled refresh rate switch which Kodi uses (whereby Kodi checks the frame rate and then changes the output refresh rate, rather than the OS doing it, which appears automatic, but is app-based not OS-based).  Netflix and Prime Video apps don't use this on the Shield TV - so they require an external refresh rate change (either using an app or the system-level 'sample the refresh rate and switch to it when you are playing' kludge)

If the current Google Chromecast Android TV firmware doesn't support app controlled switching - that's a shame.  However it's not unexpected. Google's previous Chromecasts haven't supported 23.976/24.000 fps output at all - they've been fixed at 59.94 or 60 (not sure which) with a global settings change option hidden away to switch to a fixed 50Hz (if you live in a 50Hz territory and mainly watch 25/50Hz services). They seemed to think that running at 59.94Hz permanently is 'good enough' for most users...

There seem to be very few platforms that actually do OS-level automatic frame rate switching (and that might actually be a good thing - as it falls over in some use cases).  AIUI the Apple TV 4K doesn't - it uses an app-controlled refresh rate switch too  - but it is implemented in a way that most app developers have embraced so support for it is pretty good.   Roku is the only platform I know that had automatic refresh rate switching - but because it triggered on Netflix's automatic trailers (so as you browsed shows your TV would re-sync between 24, 25 and 30fps content - giving you a blank screen and then your TV's OSD would appear) they disabled refresh rate switching entirely on Netflix (which the Apple TV app didn't do - as the app controlled refresh rate and didn't switch when you were in the menus, only when playing an actual show or movie)...