I finally got around to giving Kingdom of Heaven 4k a proper watch this evening. This UHD is remarkable.
There are a few shots where the shots were clearly less than perfect (too dim, a little soft, etc) but they are few. The rest, at least 90%+ of the movie is, I'd say, about as perfect on the video side as a film of this age can be. Film grain is present but fairly subtle and natural in most scenes - Quite nice overall. The HDR treatment is quite nice too. Bright and impactful, but rarely overly exagerated as can sometimes happens. No doubt some of the high-end, cutting edge digital filming of modern times can one-up the picture here but given the source, this is grade A/five-star worthy.
The audio side is solid too. I can't comment on the height treatment from the Atmos mix as I was watching in 4.1 with the OLED, but I had no complaints about the sound. There was a surprsingly robust low-end as well. There were a few occassions where the drums and LFE effects shook the room in a way I don't recall before.
If you are a fan of this movie, the UHD is, in my opinion, far and away superior over other versions.