I exclusively use it as UHD Blu-ray player. Also, it's from a different region than my PS4 so that comes in handy for normal Blu-rays, too.
I might dig into the Atmos app for headphones soon. So far I have always used my MixAmp (5.1 Dolby headphones that can only take DD so it's limited in the bitrate).
I also liked setting up a new device as usual. I made an account, avatar and everything. But I haven't played a single game on it yet. Just zero motivation as I have so much to play on PS4.
I don't like splitting stuff up and to me the PS4 feels so, so much better as a gaming system. It's faster and easier to navigate/jump in and out of games. There are some features/options that are handled well though.
Restmode seems to be handled better on PS4, which is my number 1 feature this gen regarding OS I think. It's a lot of small things that accumulate me not wanting to use that platform if I don't have to (i.e. shitty PS4pro not having 4K Blu-ray...). Like sometimes the controller losing sync even though I just used it to turn on the system... Annoying enough for movies already.
Still might get some exclusives some day.
Was still worth it for Planet Earth 2 in 4K and HDR.