I've been waiting for animated superhero films for adults. Well, it has started.
And it started with the best material possible: Frank Miller's The Dark Knight Returns (which oddly is the original, not the sequel.) and his Batman: Year One. (Dark Knight is in two parts, wisely.) The latter not drawn by Miller, but making the name of David Machucelli. (Who I don't think has done much since, except his Daredevil collaboration with Miller, which was also stunning.)
Both real dang good, and surprisingly, astoundingly true to the source material. (Especially Dark Knight, I've never seen an animated version being so close to the original art. Fortunately, because this was Miller's masterpiece. It has at least four distinctly different drawing styles in it, and yet it works beautifully as a whole.) (Admittedly the movie plays down the differences in those styles, understandably.)
And both available for free if you are an Amazon Prime member. (I am, they keep piling new freebies on that deal.) (Update: it appears that this is not "free" in the US, a pity.)