For me, it was a weird one. The Trial Of Peter Parker Part 3 Of 4 in Spider-Man #60.
I was really, really young when I picked this up, but from what I remember, it was jam-packed with action and destruction. I couldn't quite figure out why there was another Spider-Man on the cover along with Peter, didn't really know who Kaine was, at least up until the reveal that he was the first clone. Even when he unmasks to Peter, though, I still couldn't figure out how or why he existed. I mean, he mentions Warren via explanation, but I didn't know about The Jackal or where he even was. I also recall being a little scared of Kaine's face, lol.
I remember seeing the panel where Peter's about to unmask himself in the courtroom, but then Kaine stops him. I recall it feeling like a big deal to me and that Peter was about to make one hell of a decision. I also couldn't understand why a guy looking like Peter was in said courtroom, all the while Spider-Man was with Kaine. For some reason, I couldn't grasp that Reilly was a clone. Not reading the issues before this was a big reason for being lost.
I didn't know who stunner was and how Kaine killed Otto.
In terms of the art, I really resonated with it when I read this as a pre-teen kid. I remember thinking and feeling like, "Yeah, this is how Spider-Man should be drawn." Lean, muscular, big white eyes on the mask, the web-pits.
What about you guys?