Grimdark generally annoys me because my impression is that it takes away and flattens out a lot of things that real people do in terrible situations. Either nobody ever tries to do anything kind or helpful or they do and then automatically die or suffer horribly as a result. It's kind of the world building equivalent of torture porn, sometimes going all the way to snuff territory. And then it tries to tell you that it's just being realistic.

I think that it's okay for an author to feel, for a little while, like they've found something new if whatever it is is new to them. I tend to associate that with new writers who haven't had time to learn the genre (or with author's who think they're slumming and doing something special that none of the morons who usually write in that area would ever have thought of).