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.
Is it possible than Sam may be in love with Danny Phantom more than Danny Fenton? Is this the real reason why she acted so pissed during the Grand Finale when he briefly and willingly took away his own powers?
Vlad: sympathetic villain who deserves the love he's sought, or a jerk who lost that chance years ago and needs to get his karmic justification?
Considering how easily Tucker is corrupted by his vice and how little time he's given in Season 3, it's possible that he's secretly devising an evil plot to wipe out his friends and take over the world. He becomes a mayor by the end of the series, giving him a significant portion of power in his hometown.
A somewhat common interpretation for Danny is that has developed into a Stepford Smiler, explaining why he's remained pretty damn chipper through the whole show, especially after the events of "The Ultimate Enemy," which by all means could have (and should have) traumatized him.
This tumblr page suggests that Danielle may be a Stepford Smiler over her severing ties with Vlad and having Danny as her only family, not to mention her life alone on the streets. It also suggests the reason she doesn't stay with Danny isn't "because she had places to go" but out of guilt over the trouble she caused him.
Anvilicious: Many episodes have aesops. Many of these hit you over the head with them. Livin' Large is probably among the worst offenders.
Skulker at first was the most dangerous enemy Danny encountered, but in his following appearances, he became less and less a serious threat, only showing competence one or two times during his encounters with Danny.
Vlad also suffered from this. In the beginning, he was shown to be the most powerful enemy Danny had, being able to easily defeat Danny with one hand behind his back. However, such success diminished overtime when he encountered the likes of Pariah Dark and Vortex. Even a few times, Danny was able to beat him.
Danny himself seemed to suffer this in Season 3. Following two seasons that developed his growth as a character, the third season regressed him to doing rather idiotic things, became extremely selfish and depending far too heavily on Sam.
Sam Manson. She is a polarizing figure due to being bossy and hypocritical at the eyes of many fans, usually as a means to push her agenda. In the first episode, she temporarily forcing her Ultra-Recyclo Vegetarian diet on the entirety of Casper High. Not only is this done without the consent (or even knowledge) of her peers, but it causes a ghost to attack. When confronted with this knowledge, she prefers to keep Amity in danger for the sake of her agenda. Later, she protests a completely voluntary beauty contest. She also serves as the person who says Danny should use his powers responsibly, but she's more than content to have Danny use them to harass a car dealership because his trucks are ecologically unsound. However, her fans worship her and romanticize her (eventually canonical) relationship with Danny.
In some extent, Danielle "Dani" Phantom. Part of the fans think she is a CanonCopy Cat Sue with no interesting personality, other thinks she is an interesting character with unexplored potential.
Tucker Foley to an extent as well, some find his character to be funny and endearing, while others find him obnoxious.
Big Lipped Alligator Moment: The random iguana-ghost attack during the beginning of "King Tuck". It's never mentioned again for the rest of the episode.
Broken Base: Vlad not performing a Heel-Face Turn in the Grand Finale. Especially when in the alternate timeline in "The Ultimate Enemy" he did perform one after a decade without powers made him realize how he wasted his life.
Canon Fodder: Lots, the most famous being Dark Danny's ultimate fate.
Canon Sue: Sam Manson has been accused of this by her detractors. It doesn't help that Butch Hartman often wrote glowingly of her.
Cliché Storm: The show is a cliché storm for the superhero genre, but usually makes it all work somehow, probably because the show had a heavy emphasis on comedy; the writing made it clear that they knew it was all cliched, so at times it could come off as an Affectionate Parody of the superhero genre.
Vlad is the second most paired off character in the series. The fact that he has plotted and would commit murder, was responsible for many people getting hurt in attacks and Dark Danny in one timeline doesn't matter much to most of his fangirls. They see (as the entry puts it) a "...suave, handsome, charismatic, obscenely rich, relatively competent, with an alternate form heavily resembling a vampire and superficially sympathetic motives (he wants to make his old love interest his wife and his arch-nemesis his son): a perfect object for fangirl lust..."
Dark Danny also has his fans. Most notable thing about him is his voice and body, but most fans tend to forget he's a mass murdering psychopath that would as just as soon do this to them as kiss them... if they're lucky. Remember he is a sadist.
According to fans, the Ghost Writer is one Hot Librarian. Somewhat averted in that he wasn't evil, just overzealous in trying to teach Danny a lesson.
Freakshow, the only human character who could truly be considered an antagonist. He only appeared as the Big Bad of one episode, and the third TV movie, but is one of the more popular villains, with the general consensus being that They Wasted a Perfectly Good Character.
Esoteric Happy Ending: Butch Hartman wrote "Phantom Planet" as a means of trying to wrap the series up. However, instead of bringing finality, many see a lot of problems with it's ending. Danny's secret has been revealed to the world, but just because he saved the world doesn't mean humans who hate or hunt Danny Phantom, like the Guys in White, will leave him alone. In fact, "Reality Trip" show how Danny would deal with everyone in the world knowing his secret. Tucker Foley is now mayor, now Amity Park is governed by an underage, perverted, technology obsessed teenager with zero skills in leadership. Also, too many subplots are left hanging, from Danielle still remaining a homeless girl to Valerie still living in her poor conditioned apartment.
Also Dark Danny, whose voice acting was so brilliant it stands out in fandom. It even gained him fangirls. Also, that muscular body is a very large improvement for someone who did it in just ten years.
Sam during her temporary evil in "Urban Jungle", and Danny when under Freakshow's control in "Control Freaks".
Ghost Writer. (Although he wasn't so much a villain as he was excessive in teaching Danny a lesson about being a jerk on Christmas.)
Family-Unfriendly Aesop: The lessons Danny learns in "Phantom Planet": What you want is irrelevant compared to what the girl you like wants. If you aren't unique and different from everyone else, then you aren't interesting or worth much. Also, giving up something to protect your family and friends makes you selfish.
Everyone seems to believe that Paulina's last name is "Sanchez", but this is never mentioned anywhere in canon. Also, many believe that "James" is Danny's middle name. Also, a number are divided on if Vlad can sense ghosts or not.
Many fans are under assumption that Ember's song indicates a bad romance that tragically took her life.
Kwan also seems to be based off Kenny McFarlane, and Kenny was made Asian in Spectacular.
The episode titles "Shades of Gray" can't get into some people's minds without thinking about Fifty Shades Of Gray the novel.
During a battle with Vlad in the first episode of Season 3, Danny is shocked at how "rusty" he's apparently gotten and how easy it is to beat him, remarking throughout the fight how "you've really lost your edge." In context, it turns out Vlad's so weak because he's currently split himself into hundreds of duplicates that he's using to possess everyone in town, but considering the Villain Decay he suffered from this point onward, it sounds like Danny's Leaning on the Fourth Wall.
So Danny's having trouble controlling his new ice powers due to lack of use and needs to learn to "let it out"... Just try to re-watch the Season 3 episode "Urban Jungle" without hearing "Let It Go" in your head.
Informed Wrongness: Any argument against Sam's viewpoint. This varies from keeping the last of an endangered species in a zoo as opposed to the wild (One of a Kind), entering a beauty pageant to show how it is a "throw back to the dark ages" for women despite being voluntary (Beauty Marked) and Danny giving up his powers voluntarily to keep his loved ones out of danger(Phantom Planet).
Moral Event Horizon: The show played it oddly straight with Danny's alternate future. The whole "Dark Danny creation" scene was horrific and it horrified even Vlad, which really says something. Also see Dark Danny's first appearance where he apparently kills multiple people on screen. Ax-Crazy, indeed.
Spectra crosses this in "Doctor's Disorders', when she infects Casper High with a ghost virus, knowing that it would be fatal.
Freakshow crosses it when he reveals he lied about sparing Danny's family and placed them on a roller coaster designed with traps set to kill them, despite that he had a brief moment where he almost formed an Odd Friendship with Jazz.
Periphery Demographic: "Boy's Action Show"—yeah right, Hartman. The fangirls of mostly the teenage and college age variety eat this show up.
Rescued from the Scrappy Heap: Some changed their opinion of Danielle after D-Stabilized, as it depicted her life as a homeless clone in a sympathetic light, her presence brought out better characterization from Danny than most of what season 3 brought out and she was able to take on Vlad on her own after her body becomes stabilized.
To a greater extent, Jazz. She started out a basic older sister: self-centered, judgmental and barely got along with her brother. When she learned Danny was half-ghost and he eventually discovered she had already known his secret, her character developed. She showed greater affection for her brother, accepted her parents' obsession with ghosts (to a degree) and showed genuine skill in ghost hunting.
Romantic Plot Tumor: One of the arguments of season 3 is that too many episodes take a great deal of time around Danny and Sam's relationship when the episodes themselves weren't even about them. Frightmare and Claw of the Wild, which had main plots that had nothing to do with with Sam, were victims of this.
Rooting for the Empire: The show has a huge number of fans for the villains who are more liked than the main hero. Or at least, more liked than Sam.
Some fans attribute this to Danielle. Mostly because they considered her pre-character development Danny as a girl, though there are fans who think otherwise: see "Rescued from the Scrappy Heap" and "They Wasted a Perfectly Good Character".
Seasonal Rot: Despite the introductions of new friends and foes, the development of new powers, and the return of some fan favorite characters, many felt the third season went through a bit of this due to changing of executives, rushed or forgotten subplots introduced earlier and the somewhat weak writing plots of many episodes ("Urban Jungle" is one of the most prominent examples).
Sending Stuff To Save The Show: Five rallies from DP Fans have been held for three years in various official Nickelodeon/Viacom areas to get the show back for another season. No dice.
There was a lot of "Save Danny Phantom" fanart people drew and sent in to the studios!
Ship-to-Ship Combat: The infamous "True-Fan VS Anti-Fan" wars which basically boiled down to "Canon" (Danny/Sam) VS "Fanon" (Danny/Anyone Else) and/or "Heterosexual Pairings" (IE: Danny/Sam, Danny/Valerie) VS "Slash" (Danny/Vlad, Danny/Dash, and even Danny/Himself *Don't ask*).
Strangled by the Red String: For some fans Danny Fenton/Phantom and Sam Manson. Many will argue that Sam, who, despite her talk of individualism, demands conformity to her views, and thus, makes a poor partner to the hero.
Squick: In-universe. Danny was quite disgusted that two of his enemies had a child.
"Geez, I'm eating so fast I think I just swallowed my spork." Cue Danny intangibly pulling the spork back out of his stomach.
Strawman Has a Point: An argument against Sam's ranting towards Danny getting rid of his powers in Phantom Planet. She calls him selfish, and he actually questions why what he did was selfish. Many people have actually taken Danny's side of the argument as his reasons were justified; his wanting to be normal again was to protect his family from the ghost hunters searching for him, and in keeping with the perception that he was no longer needed as Amity's protector. It doesn't help with the above Alternative Character Interpretation for Sam.
"Double Cross My Heart" has the character Gregor want to start a relationship with Sam, while hoping not to spend anymore time with Tucker. Sam says that while "Tucker might be annoying, but he's one of my best friends, he's part of the package". However, Gregor's not wanting to have Tucker a part of his relationship with Sam was reasonable. 1) Tucker was constantly interfering with their dates and ruining the moment, 2) Tucker never stopped talking, 3) It isn't Tucker he's dating, it's Sam.
"The Fright Before Christmas". Sure Danny needed to learn his lesson about not ruining the holiday for everyone and let go of how crappy his past Christmases were, but he wasn't exactly wrong to be upset given his parents arguing the existence of Santa, to the point of not even noticing when they put their son in danger. If anything, someone should have taught THEM that arguing over the existence of Santa Claus should not be more important than making their family happy.
Harold Faltermeyer's "Axel F" as Danny surveys his parents' very 80s college campus in "Masters of All Time".
Walking On Sunshine plays as the parents depart for the fake cruise in Pirate Radio. In-universe, nobody notices that the muzak that's playing in the same episode is an easy-listening remix of Ember's theme song.
Take That, Scrappy!: Despite being the comic relief, Tucker Foley isn't that liked by several fans, finding him unfunny and never shutting up about technology or girls. In the episode "Double Cross My Heart", Sam has a new crush who seems like a decent guy, but then he finally snaps and yells at Tucker, which causes Sam to realize he's a jerk and breaks up with him. Even though he's the bad guy in this conversation, many actually agree with what he had to say about Tucker.
Gregor: Dude! Do you ever stop talking?! Do you even know how obnoxious you are with your stupid jokes and your lame-o technology? IDIOT!
In Girl's Night Out, Jazz calls out Sam for her bossy behavior and failed planning. It was a welcome thing to hear.
Tear Jerker: Seeing Danny in the alternate future. It's no wonder he wanted to get rid of his emotions.
And even then, watching the human Danny, battered, shivering and terrified about what his detached ghost half has just done. It hurts to watch the hero of the show in such a helpless and pitiful state. Everything that came before just makes it worse.
For some, the perfect clone of Danny dissolving and Vlad's subsequent Big "NO!" could be interpreted as a tear jerker. Even Danny and Dani look a little upset.
Danielle, for those who don't consider her The Scrappy. Had the series continued along with her subplot given more than two episodes, she was to eventually be accepted by the Fentons and become Danny's little sister. Considering the episode she debuted in feature Sam and Tucker tired of being sidekicks, Danielle could have easily filled this role too. Doing this might have also developed Danny's character further as a big brother and a mentor.
Remember Dark Danny? Danny's evil counterpart who was more powerful that him, had a complete lack of any sense of good in him and, considering he exists outside of time now, no longer needs Danny alive so he can easily kill the ghost boy? Did you know he was supposed to be the main villain of the season finale. Apparently Butch Hartman and the new co-producer, Kevin Sullivan, decided that we needed more reminders that Danny liked Sam in season 3 instead of bringing Dark Danny back.
Several new villains like Undergrowth and Noctune had interesting looks but botched by typical "rule the world" plots and more Danny and Sam shipping. (To be fair, Undergrowth had an excuse.)
The final episode featured a team of ghost hunters hired by Vlad called "The Masters Blasters", giving Danny a hard time and making people love them instead of him. The idea of Vlad having a team of ghost hunters working for him might have made them a decent Quirky Miniboss Squad and rivals to Danny... if they didn't appear in the very last episode.
Freakshow, the only villain in the series who is human, since the others are either a half-ghost or just amoral ghost hunters who see ghosts only as monsters, could have been a cool re-occurring villain, especially since, unlike the other humans, including Vlad, he doesn't use technology but magical items. Also, he's shown having "ghost envy" and feeling everyone cares more about ghosts than him, which made an interesting foil to Jazz, who noted the same feeling at times. He's only used in the season one finale and in the third two-parter of the series... and that was it.
They Wasted a Perfectly Good Plot: To be fair, Season 3 had some good ideas. However, it was all botched due to rushing some subplots, as well as forgetting others or not giving them proper conclusion, Vlad's Villain Decay making him less impressive as a villain as well as appearing when not needed, constant Ship Tease between Danny and Sam that even shippers felt was unnecessary and unneeded episodes (one example is Livin' Large, where Danny literally changes his opinion on being rich in the middle of the episode and becomes greedy for no reason).
Danny finally frees Wulf, but the episode this occurs in only features this in the second half of it, the first half is more of an unrelated summer camp story.
Danielle's subplot of being unstable was going to end differently, with the Fentons adopting her, instead she's stabilized by a miracle "Fenton gadget of the day" and goes off on her own again... in only her second appearance.
Valerie learns the existence of half ghosts and that her hate for them made her a pawn of Vlad Plasmius, vowing to make him pay... right before the series finale.
Also, in the episode Valerie becomes a ghost hunter, Tucker attempts to establish a relationship with her. Although she at first dates him because of his knowledge on ghosts, the end of "Shades of Grey" implies she started to reciprocate those feelings. However, by her next appearance, not only is Tucker over Valerie, he's outright rude to her. This route could've granted Tucker some much needed character development with dueling loyalties, but was removed in favor of Valerie becoming Danny's love interest.
Several people felt "Reality Trip" would have gone better if Danny didn't erase his secret identity from his parents' memory. If they still knew then Danny wouldn't have to worry about them hunting him like in "Forever Phantom" and they would have been much more helpful if they were aware, from stabilizing Dani to knowing not to trust Vlad. If anything, erasing their memory, especially when they made it clear they loved their son no matter what, wasn't restoring Status Quo so much as not letting characters develop and keep plots repetitive.
Thanks to Steve Marmel not being a part of the show anymore, many story arcs from the first two seasons were dropped. The above mentioned Danielle and Valerie stories were among them. Other examples being the return of Dark Danny and Vlad's deal with the Fright Knight. These could have been explored in season 3, instead of an episode devoted to... the Box Ghost.
The "The Ultimate Enemy" set up the possibility that Vlad might see the error of his ways one day and reform, sadly he never did.
Unintentionally Unsympathetic: A common argument against Sam in the episode "Double Cross My Heart". She is extremely angry at Danny for spying on her during her date with Gregor, despite that she did the same to Danny during his time with Valerie. Unlike Sam, Danny had legitimate reasons since they knew nothing about Sam's new crush and Danny didn't realize at the time he was jealous. Not to mention Sam is never called out for her own actions.
The Woobie: Danielle "Dani" Phantom. Ignore whether or not you think she's a bad character or a wasted one. What we see is a spunky young girl who kicks butt, then think about what REALLY happened with her. She's a little girl who was emotionally manipulated by her father to do bad things only to find out he never loved her. Then there's her second episode where she's betrayed by a person she helped and had the one person who cares about her captured. Then she's TORTURED to death by her father, who she very likely still cares about since she gave him the benefit of a doubt and asked if he found a way to fix her. Not to mention all that time between the two episodes she was effectively dying a slow, horrible death while living on the streets.