Alternate Character Interpretation: Not so much the characters as the writers. Gerry Conway has been accused by many as killing her off because he preferred Mary Jane, but the official story is that they wanted a shocking death, and Gwen was the only one who would be shocking enough. So for many fans, it's down to two interpretations: A case of Die for Our Ship, or a case of Stuffed into the Fridge. Gerry Conway himself is unambiguous
"The amazing thing was that he [Stan Lee] created a character like Mary Jane Watson, who was probably the most interesting female character in comics, and he never used her to the extent that he could have. Instead of Peter Parkerís girlfriend, he made her Peter Parkerís best friendís girlfriend. Which is so wrong, and so stupid, and such a waste. So killing Gwen was a totally logical if not inevitable choice."
Complete Monster: The Green Goblin established himself as a completely monstrous individual with this story. As if killing poor Gwen wasn't enough, the Goblin completely mocks the value of her life. The point is driven home when the Goblin gets completely pissed after Spidey (supposedly) destroys his glider, and starts to cry even harder for revenge. Spidey calls him out for acting in such an entitled way when he just killed his girlfriend. The Goblin then says the little chestnut of calling Gwen "a simpering, pointless girl who never did more than occupy space". Cue Spider-Man beating the crap out of him.
Spidey's No-Holds-Barred Beatdown of the Green Goblin after Gwen dies. Keep in mind, Spidey is sick during this fight (only a cold, but still), and yet he manages to wipe the floor with the Goblin. He was that pissed!
On a meta level, the fact that the writers managed to permanently kill a major character convincingly. Though as pointed out by Gerry Conway, the decision to kill Gwen was not especially controversial by the editorial staff.
Franchise Original Sin: In retrospect this story, while a classic and Wham Episode anticipated many problems that plagued Spider-Man in later issues, and didn't exactly provide an ideal solution.
Many say that the original impetus for the story was a way for writer Gerry Conway to resolve the Gwen Stacy romance since she had become too close to Peter and realistically, as an Official Couple, they would eventually marry and settle down which aged up the character considerably. Conway also saw Gwen as uninteresting compared to Mary-Jane and he stated later that the only reason people remember Gwen was because of her death. Conway was a decent writer and the storyline worked out pretty well, becoming a stunning Wham Episode that changed the course of the series. However, by replacing Gwen with Mary Jane, the same problem of Peter being part of an Official Couple resurfaced only now the excuse of the Love Interest being boring couldn't fly, since Mary Jane had Popularity Power, so eventually Peter did get married after all, a decision which Conway said was a mistake.
Another complaint is that writers now couldn't kill off any more of Peter's girlfriends because it would make Peter too much of a Failure Hero. Conway's idea of killing Gwen was merely a one-time solution to the problem of whether or not Peter should age.note However, writers later on killed off at least one would-be love-interest ("The Death of Jean DeWolff") and tried to sell readers on the idea that Mary Jane had actually been killed in an aircraft accident.So later writers tried to find another way to get out of this problem, leading to controversial retcons like the one in The Clone Saga and universally reviled storylines like One More Day, both being extreme ideas to keep Spider-Man from aging and freeing him from being part of an Official Couple. In some tortuous way this is supposed to have planted the seeds of Spider-Man's Dork Age problems.
Harsher in Hindsight: When at the end of ASM #122 Mary Jane attempts to console the grief-stricken Peter and mentions how she herself is wrought up by Gwen's death, he tries to brush her off by saying she would not even care if her own mother died. About ten years later she would reveal that her mother had already died before Peter first laid eyes on Mary Jane.
Like You Would Really Do It: Averted - the writers made it absolutely clear that Gwen Stacy was dead for good. The same applied to Norman Osborn until he was resurrected over twenty years later.
Love It or Hate It: The story's reception in its own time. The fans flooded Marvel with letters, some praising the creators for taking such a bold move, others calling them murderers. Nowadays, it's highly regarded.
Moral Event Horizon: The Goblin's murder of Gwen is perhaps the best known example for a Moral Event Horizon in the history of comic books. Not only because of the act itself, but because of his utter dismissal and even contempt for the value of Gwen's life.
Never Live It Down: Some fans define the character of Norman Osborn by the crime he committed in this story, and less-informed fans define Gwen Stacy by this moment/her characterization during this moment. She's almost always remembered as the Girl Next Door type characterization that she had at the time, and remembered as the 'one who died'.
Seinfeld Is Unfunny: This is the one comic that started the entire Woman In Refrigerators trend, predating the Trope Namer by a good two decades. Although most people agree that it's not an actual proto-example of it, since Gwen's death have deep, meaningful consequences to Spider-Man's character and mythos, even to this day. Conway didn't use the death only for shock value, but used it as the foundation of his entire run, exploring the effects this death has on Peter and his inner circle. The infamous trope is not named "Dropped From A Bridge" for a reason. Still, the "death of a significant other" has been done so many times in superhero stories since it first came out that it doesn't have nearly the same impact on modern readers.
Tear Jerker: Gwen's death and everyone's reaction to it.
Spider-Man: "I saved you, honey... don't you see? *quietly* I saved you..."