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 Dee Dee and even Dexter were upset at it happening. And then he comes back a few episodes later...
Quite a few fans believe he has Asperger's syndrome, or something similar.
One could argue that Dexter's Mom has a form of OCD, especially if the Mother's Day episode is anything to go by.
Dee-Dee is often seen as having a form of ADHD.
How much of this show is just happening in Dexter's head? The constant Reset Button could be an indication of this.
Is Dexter actually the smarter sibling, or just the more motivated one? There are plenty of episodes that indicate Dee-Dee actually understands all of Dexter's technology (sometimes better than Dexter does), she just doesn't have the inclination to put her knowledge to use.
Considering the somewhat unethical nature of some of Dexter's experiments opens up another can of worms entirely. Does Dexter have a darker side, is this the normal scientific train of thought, or is Dexter just a young and somewhat naive kid whose moral compass is still being formed?
Dee-Dee is seen as either a good foil to Dexter or an annoying pest. Not helping is the fact that she suffers pretty badly from Depending on the Writer and can come off as being unacceptably cruel to her brother at times.
Mandark, especially after going through horrificVillain Decay, and the fact that he appeared way too much in later episodes.
The part of "Continuum of Cartoon Fools" where Dexter holds a stopwatch while periodically saying 'BAAAAWT'. Those who have ever did timing scripts for animation dialogue 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 the fact that it was funny.
Turns out that last part was actually an animation error brought on by the Korean animation staff misunderstanding instructions from the US storyboard artists telling them that the audience should "take off" (as in leave) at the end of the song due to a language barrier. Instead of telling the animators to do it over, the editors decided to leave it in the episode and even added an accompanying sound effect to make it funnier.
The end of "Sun, Surf, and Science" in which after spending the entire episode competing for Dee Dee's affection, Mandark is saved from the surf by the surfer dude she was seeing - next thing you know, they stare longily at each other and walk off into the sunset arm-in-arm.
Over the 3rd and 4th seasons. Many fans think they're completely terrible, while some feel that the later seasons have their moments even if they pale in comparison to the older episodes.
"Dexter vs. Santa's Claws" is either considered funny for Dexter getting into a brawl with Santa or one of the show's lowest points for Dexter ruining Christmas and the episode giving the Family-Unfriendly Aesop that Christmas is only about the presents.
Many fans find "Dexter and Computress Get Mandark" to be one of the funniest episodes due to being a completely nonsensical story written by a six-year-old boy, but there are some who find the episode's existence to be a horrible mistake for the same reasons.
Cargo Ship: Dexter really loves his computer. And the feeling's mutual.
Pairing up Dexter and Blossom is surprisingly popular.
And in a lesser extent, Dexter and Buttercup - which, interestingly, is actually supported to a small degree by canon: in a vocal announcement back in the late 90's/early 2000's in during one of the credits, it was announced that Dexter has a crush on Buttercup, because she's sassy. There were even hints in a few Cartoon Network games, such as in the Cartoon Network online game "Cartoon Cartoons Summer Resort", where Buttercup pointed out the feeling was mutual, and the two danced at the disco. And their interactions aren't even Belligerent Sexual Tension either, as others would suspect.
Mandark gets this treatment a lot. It helps that he's just more of an ass than an actual villain.
Dexter is a somewhat mild case of this. Although Dee Dee is generally the antagonist, there are several episodes in which Dexter is genuinely being a jerk to her when she doesn't really deserve it, verbally abusing her when her worst crime is being nosy. He's also used her as a human guinea pig several times, including performing an unnecessary brain surgery on her for his benefit. Some viewers tend to forget that both siblings are capable of being jerks to each other and that Dexter is not 100% innocent, and neither is Dee Dee.
The shorts "Dial M for Monkey" and "The Justice Friends" are just as popular if not more so than the main Dexter shorts, in a better case, the latter.
Lisa the babysitter. She only appears in a very early episode of the series and never shows up again after that. But look up any fanart of her and you'd be surprised at how much of it there is. Guesswhy.
For similar reason The Touchy-Feely Neighbor Lady and Candi, the Dee Dee replacement, are widely remembered despite only appearing in one episode.
Mandark's abrasive younger sister and Dee Dee's rival-turned-friend Lalavava only appeared in one episode, yet has a substantial amount of fanart, enough to have gained her own category in some fandom groups for the show.
Lee Lee, one of Dee Dee's friends, is one of these
Douglas Mordecai, one of Dexter's friends, despite being a borderline Satellite Character in canon. Maybe just because he was the only character Dexter could talk to like a human being.
Val Halen has a ton of fangirls.
The Puppet Pals. Some people wished they had their own Spin-Off (the closest we got were some live-action segments featuring the duo to fill time in some eps).
The robot parrot from "The Parrot Trap", thanks to its statements making the episode one of the funniest in the show's history.
Family-Unfriendly Aesop: As mentioned under Broken Aesop above, Dee Dee once taught Dexter that he should pay more attention to his old creations and not be so preoccupied with new stuff. Seems pretty good... if it weren't for the fact that science is about making progress. It does still work in a Frankenstein fashion, though.
"Dexter vs. Santa's Claws" is still one of the most hated episodes for several reasons, one of which being the implication that Christmas is only about getting presents, and nothing more.
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). Though it's possible he did that just in case the photos had been misplaced.
Genius Bonus: A lot of gags on the show are science references, some of which are fairly obscure.
Mandark's parents are already bad enough for denying him his interest in science, but he's clearly uncomfortable with his birth name of "Susan" and how they try to overly feminize him. For LGBT viewers, it's a little uncomfortable seeing a little kid have both a lifestyle and gender role forced on them that they don't feel suits them. Mandark's rage at Dexter laughing his name is understandable because not only is it cruel, but Mandark himself even hates the name!
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.
Part of Dexter's plan to get Lisa the babysitter to fall in love with him is to turn himself into a teenager. He does so, but ends up a homely and grossly stereotypical dweeb, driving her away. Later, Cartoon Network would create FusionFall, where many of the younger characters seem to be teenagers, at the oldest. In the game, Dexter's older self is... not a gross dweeb. Farfromthat, in fact.
In an episode spoofing The Incredible Hulk Dexter turns a Hulk-like creature if he doesn't eat enough vegetables, and when denied anything from the school's cafeteria utters the line "You wouldn't like me when I'm hungry." Years later Bruce Banner actually ends up saying the same thing by accident in The Incredible Hulk.
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.
Incest Subtext: Between Dee Dee and Dexter in several episodes, though mostly on Dee Dee's part. Particularly in one episode where she's pretty much infatuated with him and even flirts with him!
Dee Dee: Hey, Dexter! Whatcha doin'?
Dee Dee: [Resting her arms on Dexter's head] Mmmmm, I just love to watch you work.
Seasonal Rot: The two seasons made without Genndy Tartakovsky after the show was Un-Cancelled due to lackluster plots (with slow pacing), Flanderization, and a new more bland-looking art style. Plus, they got rid of the Justice Friends and Dial M for Monkey segments. Oh, let's not forget that the two final seasons are about everything, butthe laboratory mentioned in the title. Most storylines of the new episodes involve Dexter playing chess, Dad playing Golf, DeeDee dying Dexter's hair blonde, and so on. In fact, the final episodes of the show are about: a) Dexter and Dee Dee learning Karate; b) Dexter writing poetry; c) Dee Dee going nuts over an ostrich.
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.
For those who don't outright hate the post-movie seasons, they're usually considered this. They're humorous and some of the episodes are more memorable than others, but overall, it's nothing special compared to the rest of the show.
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/or The Justice Friends were strong enough concepts for their own show.
Most fans agree that the Un-Cancelled seasons used hideous character designs.
Invoked with "Creepy Eyed Girl" and her Spear Counterpart. They have giant eyes that look more like a Precious Moments character than Dexter characters.
Unintentionally Sympathetic: The numerous times Dexter is depicted as a Jerkass for yelling at Dee Dee donít hold up due to the Made Out to Be a Jerkass usually being in play. Not to mention that when she isnít destroying his lab, a lot of problems are cause because of her merciless teasing of him.
Dee Dee whenever Dexter destroys something of hers for example in Down in The Dumps. The total disregard she shows for Dexterís things and even Dexter at times makes it hard to feel sorry for her, especially since a lot of those instances were in retaliation for something she did. Her punishment in "Sdrawkcab" is one of the best examples. She makes Dexter puke his lunch out, get in trouble with his mother and even sent her own father to the hospital. Her only reaction to being called out on the awful things she's done is to just stay there and smile like an idiot. If not even dangerously harming her dad makes her feel bad in the slightest, then she might as well cross Moral Event Horizon.
Unpopular Popular Character: Koosalagoopagoop is not well liked in the Land of Koos, but Dee Dee, the audience, and eventually even Dexter like him.
Dexter, for those that don't see him as The Chew Toy. And to a few that do. He's especially Woobie-ish in "Old Man Dexter" when his family excludes him from movie night because he's not old enough to stay up late.
Mandark at the beginning of "Mandarker". This was before Mandark became the show's borderline Big Bad, so it counts.
Dee Dee, sometimes. It's implied that the reason she keeps going into Dexter's laboratory and annoying him is because she wants to spend time with her brother. Many younger siblings could relate to her.