I only have a standard PS4 but it supports HDR. Horizon Zero Dawn looks a whole lot better in HDR, there is just more detail in the colors. The campfires look almost real. Maybe it's the game and not the TV. I've seen great looking HDR on this TV and not so great looking. Remember, it could be the source material, it doesn't necessarily mean the TV is doing something wrong.
Personally I think the second image looks better because the shadows are more defined, better color detail and it looks more natural. This may just be the developer's intent.
PSN ID: CrimsonNagus
XBL GT: Crimson Nagus