I'd say definitely SR1. You're in a wasteland of what's left of Nosgoth, the humans are stuggling to survive as monstrosities stalk around them. Oh, and Raz gets tortured for a subjective eternity, robbed of his (un)life, introduced to Cthulhu's grandpa, finds out his entire clan is dead and everybody else he knows has turned into an utterly inhuman monstrosity and wants to personally tear him apart. That's like a family meeting, if your family boasted teeth and super powers. And they looked like deep ones. And you found out every close relative you had has been killed. And also all of the remaining ones hated you in their guts.
Although, admittedly, BO1 is still pretty dark. It shows just how corrupt Nosgoth has become - soul stealing weirdos, sadistic vampires, Dark Eden all that stuff. I just think that Nosgoth is better than a Nosgoth that looks like like a setting for a Fallout game.
Then again, none of the games are exactly light hearted. --- We do what we must / because we can. / For the good of all of us. / Except the ones who are dead.
Like the views in Nuprator's retreat show, Nosgoth is about half-way between purity and corruption in Blood Omen 1. There were some dark, terrible landscapes (Cohagen, Vorador's swamp, Dark Eden), but there were also some beautiful ones too (the pillars, Wilendorf).
In BO1, Nosgoth is in Chaos. In SR1 the dust has already settled (a couple of times even) and there isn't much left. --- ~King of Ikari~