...or how the exterior bridge design is a direct swipe from the ship in Universal's sci-fi mini-classic This Island Earth
Ouch...are we getting a vivid image how Roddenberry told Matt Jefferies what he wanted the ship to look like? Put pictures on a wall and then say "I like this and this element from the others, combine these into a new design that has recognizable, familiar features but still looks fresh and significantly different"?
The significant differerence is that Mitchell did not isolate himself on some remote world, reject the attention of others, or find himself consumed by his own inner demons/alien technology.
I'm afraid I don't see that much of a difference. Mitchell was isolated in sickbay and started to isolate himself in his delusions of grandure, he lost his compassion for others and was in fact consumed by his inner demon aka "Number One" ("The Prisoner") and became "evil" (i.e. militantly selfish).
Alternately I could invoke "Charlie X" although this Episode is rather derivative of what we'd just seen in WNM.
My point is that both "Forbidden Planet" and the two aforementioned episodes (and to some extent "The Cage", too, because the Talos death penalty was apparently designed to discourage others from learning the superhuman telepathic powers of the Talosians...) essentially dealt with the concept that man was too imature and inexperienced to deal with such godlike powers.
I think that TNG's "Hide and Q" was a nice tip-to-the-hat to these early TOS episodes (and though somewhat naive not that bad at all).
Which reminds me of one thing: What happened to the TOS energy barrier? Unless my memory is flawed I don't recall it ever being mentioned again in TNG...maybe a Q thing, indeed?