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.
YMMV: The Iron Giant
Accidental Aesop: The Giant's emulation of Superman and dislike of the villainous robot Atomo shows the importance of role models and positive representation in media.
Fan Nickname: "Hog Hug", used by some fans to refer to Hogarth because of one scene.
Fan-Preferred Couple: The movie's fandom is infamous for fact that 99% of the Rule 34 is oedipal incest between Hogarth and his mother.
Fridge Horror: The gigantic robotic super weapon had to come from somewhere (which the movie never acknowledges). It's likely that those who sent the Iron Giant to earth are not going to just give up after one failed attempt. This deleted scene shows the Iron Giant's memory of him and an army of others of his kind destroying another planet. The fact that the creators were so willing to sacrifice an army of them also strongly hints that there are plenty more of them, too. Also, the end of the movie explicitly shows us that the robots can survive nuclear blasts. And who's to say that he's still friendly after reassembling himself?
Genius Bonus / Easter Egg: When Hogarth and the giant go out walking at night, pay attention to the moon in one scene. Just to the right of it, one of the stars can be seen to move. That's Sputnik.
He Really Can Voice Act: Vin Diesel as the Giant. He doesn't get much dialogue, but whenever the Giant speaks, the mood is absolutely spot-on.
Also, Kent Mansley saying "Screw the Country! I Wanna Live" as his final lines in the movie after he unwittingly sent a nuke directly into the town becomes extremely ironic when the President in Shadow the Hedgehog (who is strongly implied to be the same president from Sonic Adventure 2) is redesigned to resemble Kent Mansley.
For publicity, Eli Marienthal (Hogarth) did an interview with Scouting magazine Boys' Life. The magazine itself gets a mention in the film as Hogarth is showing his comics to the Giant...although not quite the one they would want.
Moral Event Horizon: Mansley ultimately crosses this when he dooms the city by firing a missile at the Iron Giant.
Remember the scene before that? When Dean told Mansley that Hogarth was with the escaping Giant? Remember how after hearing this, Mansley told the general that the Giant had killed a kid! ...Yeah Mansley, way to go.
Some Anvils Need to Be Dropped: Friendly giant robots aside, this film is very explicit in its condemnation of nuclear weapons, and of paranoia and xenophobia in general. It also drops the anvil that you are who you choose to be. Nobody programmed you to do anything; you choose who you become.
The film was universally loved by critics, but that didn't save the film from bombing at the box office; Warner Bros.' marketing blitz for the home video release (as well as Cartoon Network airing the film numerous times in the past few years) led to the film being seen by a wider audience, and now it's considered a modern animation classic.
Cartoon Network once did a Memorial Day special of airing the movie over and over and over and over and over again back-to-back, three days in a row.