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.
Apparently, it's more well-remembered than the comic strip.
It's also more well-remembered than the Ruby-Spears series.
Designated Villains: Hector, Wordsworth and Mungo whenever they appear in the Heathcliff segments.
Ear Worm: The doo-wop style theme tune is quite insidiously catchy.
Ensemble Darkhorse: The Catillac Cats. When this show aired, it was always about Heathcliff. Only his segments were acknowledged in promos and commercial bumpers (the ones by Fox Family). However, most fans of this show will agree that The Catillac Cats series was much better than Heathcliff's.
Maybe not being based on an established, but very dated comic book property had something to do with that.
Germans Love David Hasselhoff: The French have the entire show on DVD because of that. Also, there were some toy figurines of The Catillac Cats produced in France. Even a toy Cadillac car that could be changed into a hovercraft, and trailer, just like in the show. If you're lucky enough you can find these up for auction on eBay.
It helps that the show was partially made in France.
Memetic Sex Goddess: Cleo. It's hard to find a clip of the show on YouTube without seeing at least three people comment on how hot she is or how they had a crush on her as kids.