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.
YMMV: Dexter's Laboratory
Alas, Poor Scrappy: Dexter wishing away Koosalagoopagoop, and he reluctantly complies. Even if you didn't like the character, you can still feel pity for him, and tell why Deedee and even Dexter were upset at it happening.
Future Dexter's leitmotif from the Ego Trip movie, first heard when he fights the machine sentinels in the beginning of the Bad Future segment, and heard again when inspired into a Heroic Second Wind by Wimp!Dexter.
Actually if you ever did timing scripts for animation dialogue you know exactly what he's doing. Word of God says that he was timing a storyboard of the cartoon itself, yet indeed, there was no other reason to put it besides it was funny.
Fridge Logic: In "Photo Finish" when Dexter infiltrates a photo processing place to retrieve photos of his lab and comes across the alphabetical storage room, he checks every single section rather than just the one corresponding with his last name (whatever that is).
Genius Bonus: A lot of gags on the show are science references, some of which are fairly obscure.
Val Hallen is blonde, based on a Swedish god, wears black, and plays lead guitar. Skwisgaar Skwigelf from Metalocalypse is blonde, Swedish, can't find his biological father (leading him to believe he's part god), wears black, and plays lead guitar. Cue WMG that Val Hallen's his father.
In the Mexican dub of the pilot episode, when Dexter is turned into a rabbit, he adds the line"What's up, doc?" Years later, Dexter first actor from the dub becomes the current voice of Bugs Bunny.
Idiot Plot: The episode "Sis-Tem Error" has Dee Dee accidentally shutting off the lab's power and spending the rest of the episode tricking Dexter into thinking nothing is wrong by disguising herself badly as Computer, Robot and Mandark.
Jumping the Shark: Genndy Tartakovsky's departure from the series basically killed it. A horrid new art style was employed, the "Dial M For Monkey" and "Justice Friends" shorts were dropped for no reason, Mandark went through massive Villain Decay, and the writing quality in general took a nosedive.
Rewatch Bonus: Ego Trip features a clever little detail that hints at the ending. The robots that come back to the present don't attack Dexter or try to fight him even as he destroys them. The first time through, it just seems like Dexter was too fast for them. The second time you realize it's because Dexter built them and they weren't there to attack him in the first place. Dexter's egotistical belief that he had to be the one who saved the future started the whole plot.
The Scrappy: Oh, Koosalagoopagoop undeniably. Pray his antics charm you, otherwise the episode just got a whole lot more annoying.
So Okay, It's Average: Seems to be the general consensus behind the infamous "Dexter's Rude Removal" episode now that it's finally been released. Not really as offensive as expected with the amount of hype, and just generally meh.
They Wasted a Perfectly Good Plot: Some fans think the Un-Cancelled episodes had some genuinely neat ideas (like a backstory for Mandark, more focus episodes for Dexter's parents, the return of "Go, Dexter's Family Go!", etc.) that were bogged down by lackluster writing and animation.
And then there's the belief that Dial "M" for "Monkey" and The Justice Friends were strong enough concepts for their own show.
Mandark at the beginning of "Mandarker". This was before Mandark became the show's borderline Big Bad, so it counts.
Word of Dante: The infamous "Rude Removal" was made for the personal amusement of the show's animation staff as a way to let off steam from the grind of having to work on an animated children's series; it was never intended to be a regular episode of the series proper, and nor was it ever intended to be released to the public... until a few years back. Because of the subject matter, many fans keep insisting that it's a banned episode from the series, even though it was never included in the series, and as such, never banned.