The problem with The Munsters is that it was essentially a one-joke premise; a family of monsters who acted like a typical middle class American family. So once you got past the costumes and make-up, the show had nowhere to go - it was just another generic family-based sitcom.
The Addams Family was fresher because the characters didn’t just look strange; they were strange. They had a skewed way of looking at the world which gave the writers an ongoing source of material.
This is it. The Munsters were like Ozzie and Harriet dressed up as monsters.
Even still, the Addams Family TOS was only slightly better than the Munsters. They repeated the same gags over and over again, which were pretty good sometimes, but aside from a few episodes the writing was uninspired and at points it was only the Munsters with a thin layer of sophistication often blotted out by the same cheap endings with the normal visitors running away in jerky sped up motion that could have been accompanied by Yakkety-Sax.
In the 1980s they continued the series with The Munsters Today which ran in syndication from 1988-1991. They tried again with Mockingbird Lane in 2012 turning the show into an hour long drama. And in 1995 they had a television movie called Here Come the Munsters with Edward Hermann as Herman Munster. They keep trying to recycle the Munsters but it just doesn’t stick.