Despite their niece, Marilyn's, "deformity" (as a normal human, she's considered "hideous" by the standards of the Munsters), it's obvious that Herman and Lily (and the rest of the family) genuinely love and care about Marilyn—even though she's technically their niece, Herman and Lily clearly see her more as their daughter, and they and the rest have even done stuff like try to help Marilyn find a boyfriend (always with poor results, but it's the thought that counts).
Eddie once complains that his parents don't scold Marilyn like they do him, but Lily makes it clear they do so because they're worried Marilyn already has a difficult life with her looks.
Marilyn is especially close to Grandpa and her Aunt Lily. Once, when Grandpa runs away when he feels unappreciated, Marilyn is so upset she doesn't even want to leave her room.
"My Fair Munster" has Herman and Lily accidentally eat the love potion Grandpa made. The sweet part is, it simply enhances the love that Herman and Lily already have for each other.
There's also the implication that the mailman Warren and the Munster's neighbor Yolanda (a bachelor and bachelorette) find love with each other via Grandpa's potion.
The ending of "Happy 100th Anniversary", where Grandpa finds an alternate interpretation for Herman and Lily falling in love with their alternate identities at the shipyard. Despite wearing welding masks and not knowing it was each other, Herman and Lily had the pleasure of falling in love with each other all over again.
For that matter, any time Herman and Lily try to secretly do something sweet and thoughtful for the other.
"Far Out Munsters" has the family interacting with a group of young hippies renting the mansion for a weekend, and generally having a great time with them. While the episode has an element of making fun of the weirdness of the Hippy movement, it's indeed charming to see a group of people not being judgmental of the Munsters' appareance.
"Treasure of Mockingbird Lane" has Eddie really excited about his family finding treasure and striking it rich. When he declares he's going to brag about their wealth to his friends, Lily wisely advises him not to. So instead, he asks if he can use their new-found wealth to buy his teacher an apple with a diamond in it. It's awfully thoughtful of Eddie to think about his teacher and, by some spontaneous fit of kindness, decide to bestow him/her a bit of the wealth, especially when one bears in mind it's not a high-paying job.
"Cyrano De Munster" ends with Lily revealing she actually likes Herman's poems and even memorized one.
In "Zombo", Eddie starts to have hero worship for the titular television star, given his creepy and macabre appearance and personality, making Herman feel jealous. But when Eddie sees that the real Zombo isn't nearly as scary or "good-looking" as he thought, he takes it as badly as you can expect and trashes the set on television. The heartwarming part comes when the actor who plays Zombo declares he's actually glad Eddie ruined the show. In reality, he's miserable with his career and has been trying to destroy his contract for a month, and Eddie unwittingly has given him a chance to break away from being Zombo. Now he's free to follow his real passion, theater acting. The cherry on top is when the actor gives Eddie heartwarming advice: "Eddie, don't grow up to be like Zombo. Grow up to be a nice, normal human being... like your father."
In "Low-Cal Munster", Lily's biggest objection to Herman going to an army reunion is that it will be the first time they've been separated in a hundred years.
Herman and Lily set the standard for TV couples, showing that a healthy relationship will have their occasional ups and downs and disagreements, but ultimately is made of two people who genuinely love being together, respect each other, make jokes with each other, and show that romance doesn't have to necessarily be hot and sweaty passion but sweet affection and little gestures like a thoughtful bouquet of weeds (although Lily does sometimes hint at having that passionate side!).
The whole reason Herman has been losing wrestling matches in "Herman the Great"- which he's taken as a second job to save up for Eddie's future education- is because his opponents are worse off than him financially and keep telling him about their families' various money troubles.
"Yes Galen, There Is A Herman" has a rather sweet bond between Herman and a young boy who's a bit of a Nightmare Fetishist. While the whole thing reeks of Values Dissonance in modern Too Smart for Strangers days, it says something that being invited to Herman Munster's house has far more innocent implications than it would a real life adult.
How did Eddie, who had previously struggled to do well in track, manage to win the race? He was so determined to not disappoint his dear old dad, who had been trying to coach him.
At least one episode had the Munsters find a suitor for Marilyn who was not scared off by them, unlike most of her suitors. And he was kind to them and treated them like people. Then he and Marilyn go out on a date. Although later episodes make it clear that their relationship didn't work out, for unspecified reasons.
Film
In the trailer: Herman thoughtfully brings Lily a bouquet of black calla lilies, which a careful look shows she put in a vase during their dinner date.
Herman and Lily are very sweet together, falling for each other very quickly and being soft towards one another in nearly all their scenes.
