Could just be the hype didn't meet your expectations, which can make a show seem even worse. It can be difficult to go into anything late, when you hear so many good things about a show/movie that put in sky high expectations whether you are conscience of them or not.
There have been a handful of movies like that over the years for me, but the only one I can recall off-hand is Kingdom of Heaven, Directors cut. I never watched the movie before and jumped straight into the directors cut thinking that it would be great, not having been tainted by the original. It was a fine movie, but not one I want to watch more than once...
As for Firefly, I didn't watch it when it aired, but more like ~2010 - 13, when there was good word of mouth but not seemingly revered like it is now. I liked the show a lot, for what it is. Can't think too hard about the space aspect of it. I also watched Firefly before Babylon 5 and The Expanse, both of which take some of the shine off Firefly as a space show.
