A bunch of odd-looking immigrants in America of a minority background who try to assimilate and don't understand why the natives there treat them so badly. Think about it.
The children who were either born in America or came over very young struggle less to fit in, which does tend to happen in real life. Eddie has lots of friends and doesn't seem to face strife as much as his parents; Marilyn balances keeping her family's culture while embracing the new world's ways.
Marilyn has gotten flack over the years for being such a one-dimensional character. She's nice, yes, but not much else. But given that she's the "ugly" one in the family, she probably realized the best way to get people to ignore her apparent ugliness is to be nice, do as little to get attention or make waves as possible to fit in better.
"Herman the Great" used to rub one the wrong way because of how much flack Herman was getting from both the wrestling fans and his own unknowing family as being "a bully" and "a coward". But then it occurs: Herman is playing the Heel! He's meant to be hated by the crowd so they can have someone for the Face to triumph. So it becomes, in a way, awesome unto itself that Herman can do a good job at his job just by being himself (showing leniency to every wrestler who claims they have a family to feed).
Remember "Love Locked Out" where Lily described her husband as a "No Account"? In the movie "Munsters, Go Home", Herman's British Uncle wills to him the title of "Lord Munster". Guess Herman's an actual Count now.
In "Munsters, Go Home", one thinks it's mean-spirited of the boys in the British village to throw tomatoes at Eddie, and (beyond accidentally hitting Mr. Moresby) they never get truly punished for it. However, one realizes they're meant to establish that the Munsters (at least our Munsters) could never feel welcome in that village, especially when Effigie and her kids already give a bad name to Herman and his family. It sets up that their place is back at Mockingbird Lane.
Often in vampire stories, weird things happen around vampires and their lairs, as popularized in "Dungeons and Dragons" and movies like Bram Stoker's Dracula. Weird things like perpetual thunder storms, strange fogs, ghostly apparitions, abundance of vermin happen around a vampire's lair, for instance. And wouldn't you know it, two vampires, Lily and Grandpa Munster (aka Dracula) live in 1313 Mockingbird Lane where perpetual thunderstorms and ghosts abound.
Grandpa has been married to different woman, and can shapeshift into a wolf. He probably married a female werewolf at one point, given that his son Lester is thr wolfman. Eddie's nature makes perfect sense.
Why does the family always seem hard up for money? Well, they would be, with Herman always accidentally damaging the house with his clumsiness.
In the 2020s film, Lily's money-obsessed conman brother Lester dresses in suits with flashy jackets like a game show host, which have cash prizes and usually have hosts with slick, used car salesman personalities.
Herman has a slightly cracking voice in the remake. Of course he does; he was only born not that long ago!
In the Rob Zombie Film, it makes sense both Herman and Lily fall in love and marry quickly: Herman hasn't even been alive that long, and we see his "father" cares so little for him that no doubt he couldn't be bothered to teach him anything; as for Lily, her father has been married so many times that no doubt she grew up with somewhat naive ideas about marriage. Or she may be determined to prove to herself that she can have a healthier marriage than the ones her dad had.
The Count marrying Zoya, a human woman, really isn't as odd as it looks. He's got two children of a different species; he probably finds quite a number of different women attractive.
Marilyn is named after beauty icon Marilyn Monroe, who was a hit star at the time. But Monroe was also a bit misunderstood and struggled to keep a relationship. The name makes sense in more ways than one.
Lily mentions in Munster Go Home that she's been stabbed with a stake several times. Lily is a very kind person in spite of her appearance, so how was the rest of the family who are also pretty nice people treated? Is there any wonder they decided to move to America?
It really makes you wonder exactly what happened to Marilyn's parents, that she had to be sent to live with her extended family in America.
The Munsters believe they live around very ugly, very rude people (it's the only explanation for why these weirdos always run away and behave oddly!). They still do their best to make friends with them and assimilate into their community, and feel hurt when their attempts to branch out appear to be rebuffed.