These are a nice addition, but are not fully supported by Arnold GPU. HDRI Lights lets you place HDR photos of real-world lightsources that dynamically update the scene.HDRI Environment controls the positioning and final look of the environment both in the viewport and the final render.Most of the ‘new’ viewport move towards ‘PBR’ is really just hacks of existing old technology code. Also, there is no background switcher in the viewport so it results in multiplied light and a horrible ‘sheen’ and rim light that shouldn’t be there. These are just high-level material wrappers on top of the Physical material, so they are not new materials at all. The two types of maps, PBR Material (Metal/Rough) and PBR Material (Spec/Gloss), ensure compatibility with any real-time engine workflow.New PBR materials make the interaction of light with surfaces physically accurate.

Also, the UI/UX is clumsily designed by engineers and is more like a beta(which it still sort of is) New BTT(baking to texture tool to replace legacy RTT) doesn’t yet support Arnold normal map baking so you have to use Scanline.

Extensive renderer support including Arnold.New tool for baking maps and surfaces offers faster performance in a new streamlined workflow.What they don’t mention in the release notes:

3ds max licence price