Regarding the tonal shift I think this kind of goes for Star Trek as well.
The first film was in a few ways a tonal shift from TOS, although it did stay close to many of it's themes it was considerably less humorous/adventurous than many of the TOS episodes. Wrath of Khan pretty much switched to a more action and event-driven style for the films.
TNG's first two seasons also were largely different in tone than the rest of the series.
In both cases Roddenberry was largely in charge, but then "kicked upstairs" so to speak.
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