These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Not so much the characters as the writers. Gerry Conway has been credited 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, its down to two interpretations: A case of Die for Our Ship, or a case of Stuffed In The Fridge.
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.
Not to mention, Mary Jane's Character Development shows brilliantly when Peter, in his despair, lashes out at her and tells her to leave him alone. She refuses.
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, Purity Sue type characterization that she had at the time, and remembered as the 'one who died'.