Now that it's been almost 20 years it's safe to say, I think Firefly was over rated. At the time it was an interesting concept, but with others doing the same idea as good or better (space western) it feels really dated.
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The same is true of a ton of popular, critically acclaimed shows several decades old.
Agreed, but Firefly was a show written around and about those tropes, where many popular shows use tropes as a method of telling a story. Joss Whedon loves using those tropes as a crutch, and he does it well, but those kinds of things never age well.