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.
Broken Aesop: Could also count as one, when you realise that all Klaatu's people do is threaten Earth to become more peaceful by announcing that they hold the Bigger Stick. In other words, exactly what the various human nations were trying to ensure through the threat of nuclear deterrence.
False Utopia: The people that Klaatu is representing can be seen as living in one. They have given over complete control of their lives to robots like Gort and have no way to revoke the decision, meaning that are peaceful not because they choose to be, but because they are forced to, otherwise they'd be wiped out by their own creation. Klaatu even promotes this as the right thing to choose, because it works!
Director Robert Wise later said that while most of the Christ allegories were intentional, the use of the name "Carpenter" was a coincidence that he never noticed until it was pointed out to him years later.
Hilarious in Hindsight: There's a scene where two doctors are discussing Klaatu's physiology, and one mentions that Klaatu supposedly has a life expectancy about twice that of a human. As they speculate about what medical advances might be responsible for this, one of them produces a pack of cigarettes, and they both light up.
There's also a scene in which a news bulletin is heard talking about Klaatu, in which the announcer speculates the two most likely candidates for his homeworld are either Mars and Venus because those are the only two planets capable of supporting life... we now know that Venus is most definitely not capable of supporting anything what with the runaway greenhouse effect that makes it hot enough to melt lead, and none of the many probes we have sent to Mars have ever produced solid proof of any kind of life, let alone something intelligent enough to develop interplanetary travel, despite very thorough searching and more clear maps of the planet than we have of Earth.
Narm Charm: Gort visibly creases at the knees when he walks, rather spoiling the illusion of an all powerful robot, but the film is good enough that you just don't care.
Unless you realize that Klaatu's society itself is based on paranoia (Irrational fear of any society that believes in self-defense) and violence (infractions are punished by having one's homeworld destroyed). Then it completely falls apart.
Not really. Humanity has a history of justifying violence in self-defense or other excuses. Klaatu's society has a legitimate fear mankind would come to the stars, find other races, and immediately start fighting them. Humanity has a whole has a habit of doing that regardless of culture so destroying the entire race solves the problem.
Special Effects Failure: Gort visibly creases at the knees when he walks, rather spoiling the illusion of an all powerful robot.
Also note the obvious wires holding Helen up when Gort is "carrying" her (the actor playing Gort was tall but not very strong, and simply couldn't carry her on his own).
Strawman Has a Point: The humans are lambasted for "striking first", but the craft landed with little warning in a capital city, Klaatu walks directly at the humans with an object held up that snaps open unexpectedly within melee range — and didn't expect humans to flinch?
They Wasted a Perfectly Good Plot: Unfortunately the film loses the Wham Line from the end of the original short story, where the protagonist fearfully begged Gnut (Gort) to relay to his masters that what happened with Klaatu was an foolish accident and the people of Earth meant them no malice.