Originally Posted by
Huntsman Spider
Marvel Knights Spider-Man #1-12 by Mark Millar. It added some pretty solid dimensions to Peter Parker's ongoing blood feud with Norman Osborn, paralleling and contrasting them in that both held the other responsible for the deaths of their respective offspring (Norman's son Harry died trying to finish what his father started, Peter's daughter was stillborn as a result of Norman's machinations) and saw each other as having wasted their potential contributions to society on petty costumed adventurism, though where the contrast between them came in was, as Norman himself put it, "I don't give a rat's ass." That perfectly and succinctly summed up the difference between them, that as flawed as Peter was and could be, he cared about those around him, maybe too much for his own good, and Norman simply couldn't care less about anyone that wasn't himself, with even his anger about Harry's death being more rooted in resentment for losing his legacy rather than losing a son.
Marvel Knights Spider-Man by Mark Millar also featured a more world-weary and somewhat more cynical version of Peter, who retained his values and morals, but nonetheless displayed, at least in his thoughts, a growing sense of disillusionment with costumed heroism and the cycle of (costumed) violence he felt himself trapped in by his own sense of responsibility. Of course, that weariness and cynicism would die down somewhat at the end of the story when Aunt May, having been rescued from Norman's latest plot to mess with Peter, showed Peter a website tallying the number of lives he'd personally saved as Spider-Man, a number at least six digits high.
Finally, Marvel Knights Spider-Man by Mark Millar came up with a somewhat plausible meta-origin for the supervillains that had emerged with the dawn of the modern superheroes thanks to Marvel's sliding timescale doing away with the Cold War as an easy source of rivals and enemies. Namely, the supervillains were really products of a conspiracy by corrupt industrialists and politicians to preoccupy superheroes with more immediate threats to the public so they wouldn't turn their focus and abilities to resolving the greater problems of human society or to the greater crimes committed against that society by those same industrialists and politicians. Naturally, one of them was Norman Osborn himself, at least until he went nuts and decided to become a supervillain in his own right.
The first paragraph, on its own, would be decent enough in a standard Spider-Man vs. the Green Goblin story, but there were elements of added maturity in the course of this particular saga. For one, Peter's musings would frequently center around how tired he'd become of the same old vicious cycle between him and his enemies and how much devastation and trauma it had brought on his life and the lives of his loved ones, especially Mary Jane Watson(-Parker) and Aunt May. Speaking of Mary Jane, though, the story did address her relationship with Peter and her relevance in his life somewhat more seriously than had become standard, especially given she obtained a gun for self-defense despite Peter's initial objections, and it came in handy insofar as wounding Norman Osborn and actually catching him by surprise when he tried to repeat what he did to Gwen Stacy with her. Then there was the portrayal of Peter's erstwhile love and crimefighting ally Felicia "Black Cat" Hardy, who was treated with a surprisingly refreshing amount of complexity, particularly regarding her feelings for Peter and her interactions with him and Mary Jane. Even a number of Spider-Man's rogues, who had somewhat fallen by the wayside and come to be treated as irrelevant has-beens and jokes in many cases, were reemphasized as deadly enemies for him, especially when organized by Norman Osborn near the climax of the story to take him down once and for all.
All in all, Marvel Knights Spider-Man #1-12 by Mark Millar wasn't necessarily the usual kind of Spider-Man story, but in my view, it was still true to his character, even with a more "adult" framing. Probably the best thing Mark Millar ever did for Marvel.