What do you mean by "dark" ? There's so much that can hide behind this sole word.
Is it "gore dark" like in
Desert Stalker, or "mad max dark" like in
Hot Sand of Antarctica ? Note that both darkness are present in those games, but each one have more of the darkness I linked to it, than the other. Or perhaps is it "thriller dark" like in
Hillside ? There's other possibilities, but no names cross my mind to illustrate them ; "sadness dark" by example, like in Dickens books.
And of course, what is or not dark also partly depend on the player. Being a widow, there's two/three games that feel dark for me, because they focus too much on this part of the story, while depicting it way to accurately.
This being said, personally I tend to avoid the game when the story is too unfair for the main characters (not specifically just the MC, but also the characters that are the center of the story). Seeing someone's life goes from Charybdis to Scylla would goes against the entertainment I search while playing. If it was what I wanted to do, I would just have to look at the mess the world is actually in.
But the real problem I have with "dark" stories is that, too often, this darkness is nothing more than a cover-up for a poor story plot. It's not really a dark game, but look at
WVM by example ; at least before rewrite, we will see what it became. Each in-game day have it's terrible fate, that will be resolved at the end of the day ; generally by a "Deus Ex Machina"-like move. But if you remove this, the game would be nothing more than the boring story of the nicest and more charismatic guy in the world. The MC would fuck anyone who ask him with puppy eyes, by fear to break her heart if he don't ; and like all girls look at him with puppy eyes... Or, on an effective dark side, The Guardian (now hit by the rule 7), that wouldn't even have a story without all the fucked up things that pill up update after update.