Like most modern historical movies, this has a very dark and ugly feel.
Compared to an older Mountain Man film like Jeremiah Johnson, The Revenant feels more like a horror film or the Orc scenes from LotR. Everything's dark, gloomy and the people look like they are trapped in Hell. Jeremiah Johnson felt far more authentic. Jeremiah Johnson also showed the dangers and unpleasantness of that kind of life, but maintained a realistic look without veering off into a comic-book style Hellscape.
A lot of modern historical films go for this mega-bleak despairing tone. The days of realistic adventures set in the past are over, I guess. Now, history is always seen as dark and morbid like a horror film or an edgy graphic novel.