These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Cab Calloway's "Minnie the Moocher" number, from the eponymous short.
Cab Calloway's "The Old Man of the Mountain", once again from the eponymous short.
"St. James Infirmiry Blues", sung by Cab Calloway in "Snow White".
"You Gotta Have Pep", sung by Betty in "More Pep".
The entire "Hells Bells" music number from "Red Hot Mamma".
The "How'm I Doin? (hey hey)" number from "I've Heard".
The title songs of the shorts "Mysterious Mose", "Barnacle Bill" and "Any Rags?"
Ensemble Darkhorse: Betty herself in the old Bimbo cartoons, and it was her popularity that caused her to ascend to stardom while leaving Bimbo (the main character!) to fadeintoobscurity.
Betty's grandpa, Grampy, who was a minor recurring character, is quite well liked by fans of the series, and considered one of the few good things to come out of the later Betty Boop shorts, mainly due to his off the cuff inventing nature and jovial personality making him very likable and gag friendly. He even headlined a Color Classics short "Christmas Comes But Once A Year" by himself!
Esoteric Happy Ending: In "Making Friends", Pudgy ends up doing exactly what Betty wanted him to do—"Go out and make friends with the world." Unfortunately for Betty, his newfound friends happen to be a batch of rascally wild animals who proceed to tear apart Betty's house upon arrival!
The Scrappy: Pudgy the puppy, Betty's pet dog from the later shorts. He is widely disliked by fans of the cartoons, mainly for his overbearingly cloying nature and lack of any personality, and having many shorts centered around or co starring him didn't do the series any favors.
Replacement Scrappy: Is often seen as a very bland replacement of Betty's more vivid boyfriend, Bimbo the Dog.
Fearless Fred is also seen as this, being a very one dimensional heroic love interest to Betty.
Seasonal Rot: Once the Hays Office cracked down on the series in the mid 30s and Paramounts management forced Fleischer to make their works more family friendly, the Betty series went into a steep decline, with the shorts becoming much more dull and generic, and the Fleischers inability to add any interesting new elements to the series (barring Grampy) didn't help.
Seinfeld Is Unfunny: Next to figures like Jessica Rabbit, it's hard to imagine a time when Betty Boop was considered genuinely racy and provocative. This is lampshaded in the film itself, where Betty (who is now waiting tables) nostalgically notes that "I still got it!" next to one of Jessica's performances.