https://www.dsogaming.com/news/diablo-4-details-leaked-prior-to-official-reveal-darker-and-grittier-will-be-similar-in-style-to-diablo-2/
"Diablo 4 is going to look dark, gritty and gross. Locations will be toned down, infrequently laid with corpses, wasteland, grey-ish deserts, clut caves surrounded by flesh, rotten crypts, marshes and bogs, as well as plagued cities. These levels will be larger than Diablo 3’s levels.
Characters will now be able to ride horses (possibly other mounts) and there might be contextual interaction with environment. Blood splatters will also look more like blood and not splashed jam."