Its a space themed middle ages plot that has been done to death, the music isnt that good in my opinion, and the characters and acting is just bland. And that Spike used to do marathons of it all the time.
I tried to get into Star Wars when I was younger, but none of the films never really "clicked" with me personally. As for Star Trek, I like Voyager and Next Generation but haven't really seen a whole lot of the other series to form an opinion on them.
Edit: *Checks calendar* ...Oh no. *Hides in bunker*
Aren't most of the "space themed middle ages plot"s ripping off Star Wars anyway? I feel like the success of Star Wars is one of the major reasons there are so many, as I think there were much fewer when it first came out.
Personally I feel the original three are fantastic. The prequels were mostly meh, the sequels tried too hard to be the originals, and Rogue One is just...ugh.
At any rate my favorite part of the Star Wars franchise will forever be Lego Star Wars: The Freemaker Adventures.