History YMMV / TeenageMutantNinjaTurtles2003

* ScienceMarchesOn: In “Sons of the Silent Age,” April, Casey, and the Turtles stumble across a nuclear power plant which they are happy to see close due to their environmental cost, and Don even gives this speech:
-->“Ah yes, nuclear power plants. Once heralded as the future of energy, but they’ve become the Purple Dragons of energy production: hard to clean up after and even harder to get rid of…”
That was 2005. Today nuclear power is once again heralded as the future of clean energy. Numerous advancements in the design of reactors have made them safer than working in a coal mine and more environmentally friendly.[[note]]The 2011 Fukushima Disaster was due to the tsunami and earthquake causing an electrical grid failure and plant operator (TEPCO) failing to meet basic safety requirements such as risk assessment, preparing for containing collateral damage, and developing evacuation plans.[[/note]] There are now portable reactors. However, the debate surrounding nuclear power still remains.

** April and Donnie receive a lot more attention than [[OfficialCouple April and Casey]] do.

* MemeticMutation: The fact that Leo rides a scooter and Raph knows how to knit are both still popular jokes among the fandom.

** Leo's character in Season 4, where for most of the season he takes on an aggressive, take-charge attitude, in lieu to the fact that he and his family technically lost against C'hell Shredder and Karai in the final battle of Season 3 and were only saved thanks to the Utroms arriving just in time to save the day. Thus, he takes any failure in the season pretty hard and lashes out ("Dragon's Rising" in particular where he chews out his brothers and Casey just because they only stopped ''half'' of the weapons cargo the Purple Dragons had stolen rather then all). On one hand, most did like that it was part of his character development in eventually learning it's okay to fail if you give it your all long as your survive and learn from it. But others fans likewise hated that they had to wait for most of the season for it and had to put up Leo's demeanor in the meantime, making it hard to watch since he was always angry and feeling TheReasonYouSuckSpeech was unwarranted since they did ''try'' their hardest (not helped with Raph ''agreeing'' with him[[note]]Although, Raph agreeing with Leo's assessment doesn't mean the viewers are supposed to agree with it, Raph is not the best judge of character and in "Cousin Sid", he not only said he likes this new, aggressive Leo (before he started going too far in later episodes) but he also [[InnocentlyInsensitive joked that they should let Karai stab Leo more often]][[/note]]). Though ironically, this was foreshadowing to the lesson Leo needed to learn later on.

** Leo's character in Season 4, where for most of the season he takes on an aggressive, take-charge attitude, in lieu to the fact that he and his family technically lost against C'hell Shredder and Karai in the final battle of Season 3 and were only saved thanks to the Utroms arriving just in time to save the day. Thus, he takes any failure in the season pretty hard and lashes out ("Dragon's Rising" in particular where he chews out his brothers and Casey just because they only stopped ''half'' of the weapons cargo the Purple Dragons had stolen rather then all). On one hand, most did like that it was part of his character development in eventually learning it's okay to fail if you give it your all long as your survive and learn from it. But others fans likewise hated that they had to wait for most of the season for it and had to put up Leo's demeanor in the meantime, making it hard to watch since he was always angry and feeling TheReasonYouSuckSpeech was unwarranted since they did ''try'' their hardest (not helped with Raph ''agreeing'' with him). Though ironically, this was foreshadowing to the lesson Leo needed to learn later on.

** Leo is sullen and silent at the beginning of "People's Choice," refusing to join his brothers in exploring the old mill. But when the other three race each other to the roof of the mill, only to find Leo already up there, ''still'' sullen and silent, and never indicating why he was there at all (he seems to only notice the spacecraft when the others do), it plays off a bit weird. It's hard to tell if it was his way of joining the fun despite his mood, or if something prompted him to climb to the roof separately, or if he was just really determined to force the others to deal with his bad mood.

* SalvagedStory: Starting with the "Season 4" DVD [[note]]which didn't actually contain all of Season 4, just most of the back half, and what's more egregious is that a commercial titled it "The Complete Fourth Season"[[/note]], 4Kids finally transitioned into selling more complete season sets of the series. Unfortunately, only Seasons 1-2, 5, and 6 saw full releases in this more consistent thirteen-episode set format, with Seasons 3 and the first half of Season 4 remaining only available in the various five-six episode DVD's from 2005-2007 - or not at ''all'' for Season 7.

** ''Fast Forward'' shifted the Turtles to the future and went for a more [[LighterAndSofter lighthearted]] tone and entirely new supporting cast, suggesting an attempt to gain new viewers, which alienated fans who preferred the darker prior seasons, but the season often referenced plot points and characters from prior seasons who understandably [[PutOnABus weren't present]] due to the shift in setting (or in the case of Bishop and Baxter, were present), which left it [[ContinuityLockout difficult]] for newer fans to get into.

** While the sentiment isn't universal, the sixth season, ''Fast Forward'', became a little better regarded over time than what it used to be back in the day. At the very least, it's seen as having an interesting if flawed concept that didn't fully get to grow and blossom, especially with regards to Space Usagi, the [=TriShreddatron=], Leatherhead coming back, and the Dark Turtles making a full HeelFaceTurn in the unproduced ''FF'' episodes. And there were at least a few characters from this season who became popular enough that fans would like to see them in future installments such as Viral and the Dark Turtles or who ''did'' appear in future installments like the IDW series (ie: Dunn, Jammerhead, Torbin Zixx) but with the benefit of better writing. While very few people would list ''Fast Forward'' in their top five list of Ninja Turtle stories or installments, the season these days is being judged a little more fairly and enjoyed on its own merits rather than being compared to the previous Mirage-inspired seasons. And to really put things into perspective, even up to today, practically nobody is clamoring for ''Back to the Sewers'' characters like Khan or the Green Mantle to make any sort of comeback and those characters have largely faded into obscurity, whereas now fans are much more open to ''Fast Forward'' characters and concepts making their way into future ''TMNT'' media and ''ComicBook/TeenageMutantNinjaTurtlesIDW'' has given a chance for some of those characters to have a second go in a new medium..

** "Insane in the Membrane" being pulled from airing resulted in some plot elements of "Good Genes, Part 1" confusing viewers at the time, namely [[spoiler:why Stockman needs to be resurrected from the dead, and why the Turtles have the helicopter he used in that episode.]]
** A unique example took place in the Season 6 episode "The Journal." Due to the fifth season being put on hold so the sixth could air first, first-time viewers were caught off-guard when the episode depicted characters and settings that had only been introduced in the fifth season. [[spoiler:Nano is seen as a member of the Justice Force, and the Ninja Tribunal are seen outside of their distinctive Shredder armor, when they had not been unmasked by the Season 4 finale in which they'd last appeared. Karai's apparent HeelFaceTurn is less obtrusive since the journal's contents were fabricated, but it still might tip off a viewer that Karai ends Season 5 on an ambiguous note.]] The appearance of a Foot Mystic also took viewers off guard given their last scene in "Good Genes, Part 2," but at least that is explained as [[spoiler:Splinter simply chucking them into the story at random.]]

* ItWasHisSled: The Shredder in this series being an alien in a mech armor suit, namely the Utrom Ch'rell.

** Even to this day, there are fans who loved the twist of making the Oroku Saki Shredder the cover identity of Ch'rell and those who feel [[TheyChangedItNowItSucks the cartoon royally screwed up by radically altering his character]]; the fact that the show later revealed the Oroku Saki Shredder was very much alive and a real person whose identity Ch'rell stole was likely an AuthorsSavingThrow in this regard. There's also if he was a cool villain whose ArchEnemy status to the Turtles was deserved or if he was too overpowered and overly prominent, the latter of which probably isn't helped by a majority of the first three seasons' conflicts eventually revolving around him.

** The Demon Shredder. The Cyber Shredder is a borderline example, being a AI copy of the original with no really distinctive features on his own besides living inside cyberspace. The fact that his existence indirectly leads to the death of [[EnsembleDarkhorse Viral]] is another black mark.

** The fact that despite being a genocidal maniac who wanted nothing more than to return to the stars to begin his conquest anew, Ch’Rell still decided to take in, raise, and train an orphaned human girl out of no known reason other than simple altruism. This has left an impression on fans years after the series ended as they were left to debate his intentions and what this says about even the most vile incarnation of the character to date.

* FanPreferredCutContent: While ''Fast Forward'' is considered to be a divisive season, many would have preferred a second season to it compared to what ''[[SeasonalRot Back to the Sewers]]'' brought as it would've featured Ch'rell taking over the body of a dead Triceraton soldier which would've likely had ''Fast Forward'' to be more in-line to the earlier seasons.

* FranchiseOriginalSin: One of the bigger criticisms of later seasons is the Shredder tends to become the center of the conflict, often to the extent of pushing other, more interesting villains who were driving the plot up to that point out of the spotlight. In spite of this, Season 1 had this issue, with a number of subsections of the Foot Clan showing up, or revealing the villain of the episode had been working for the Shredder, but at that point, the Shredder was the only major antagonist in the series, so it wasn't as much a problem because most of the villains at that point lacked depth.

** Torbin Zixx from ''Fast Forward'' tends to be rather disliked by fans due to all three of his appearances largely boiling down to conning or swindling the Turtles, being a condescending SmugSnake, going unpunished for a long period of time before KarmaHoudiniWarranty finally set in, and having little-to-no redeeming qualities.

* EnsembleDarkHorse:
** Hun and Bishop, to the point of becoming [[CanonImmigrant Canon Immigrants]].
** Usagi and Gen are both really popular and tend to steal the show whenever they show up.
** The Dark Turtles for their cool designs, personalities, and interesting subplot hinting at the start of a redemption arc in their final episode.
** Viral is quite popular among the artist community, due to her unique design and being the lone villainess in ''Fast Forward''.
** Chrysalis is probably the most minor member of the Justice Force and never even says a word in the series, but is well-remembered by many.
** Traximus, the Triceraton gladiator who becomes FireForgedFriends with the heroes and the RebelLeader against his oppressive government, is seen as a highlight of the three arcs he appears in.
** Kirby King, the artist whose drawings come to life, is impressively popular for a OneShotCharacter. It helps that he's modeled after the late Creator/JackKirby.
** Eventual Justice Force member Raptarr is the subject of a decent amount of attention, fan art, and {{Shipping}} fics due to his appearance and powers, his IdealHero nature, and the interesting BackStory of his species.
** The Battle Nexus competitor Rings only appears in one episode and is eliminated after a fight that lasts about a minute. Still, his cool use of {{Deadly Disc}}s and his BarbarianLonghair appearance earn him some fans.
** In a meta sense, this version of April is generally better liked than the other versions that aren't Channel 6 reporters.

* HilariousInHindsight:
** In "Shredder Strikes Back, Part 2," Raph flashes back to the Shredder's (first) defeat, and states that "Nothing human could have survived that!" Much later, it would be revealed that the Shredder ''isn't'' human.
** In "Exodus," it was promised "[[WhamEpisode One of these characters will never be seen again]]", and after the episode, Ch'rell is banished to an ice planet, likely never to be seen again... That is, until ''WesternAnimation/TurtlesForever'', but even before that, Peter Laird confirmed that the Triceraton Shredder shown in concept art of a possible second ''Fast Forward'' season would have been Ch'rell hijacking the body of a Triceraton soldier, and ''Back to the Sewers'' not-so-subtly implied in its first episode that Ch'rell would fight the other two Shredders in the show (there would have been an arc called "The Shredder Wars"), making the claim that Ch'rell would never be seen again ''hysterical''.
** On a similar note, there's this exchange, from Season 5, before the Cyber Shredder was introduced (and, consequentially, before ''WesternAnimation/TurtlesForever'' and the whole 'Multiverse' thing).
--->'''Mikey:''' "Real Shredder," "True Shredder," "Utrom Shredder..."
--->'''Donnie:''' How many Shredders ''are there''?
** Early on in Season 1-- the episode "The Garbageman"-- Mikey tries out several catchphrases, much to his brothers' distaste. One of those catchphrases is "It's trench-coat wearing time!". Nobody (except the fans) seems to have a problem with "It's ''ninja'' time" five seasons later.
** The Dark Turtles from the ''Fast Forward'' season have far more distinct designs than the Turtles, with Dark Leonardo having the most balanced physique, Dark Raphael having a bulkier form, Dark Donatello being taller and slimmer, and Dark Michelangelo being somewhat smaller than the rest. Barring Michelangelo, almost all of the design traits are exactly like [[WesternAnimation/TeenageMutantNinjaTurtles2012 the 2012 incarnation of the Turtles]], who [[DivergentCharacterEvolution were all made distinct aesthetic]]-wise. Dark Raphael also has spikes protruding from his body and shell, which also makes him resemble [[spoiler:Raphael's mutated pet Turtle Spike, who would become the 2012 incarnation of Slash]].
** "The Return of Nano" has a bit of back and forth on NotADate between Casey and April. During the climax, Donatello needs April's help for his plan and runs off with her, leading Casey to bemoan "that sneaky, little green nerd" running off with his date. This exchange got funnier in light of the three characters being in a love triangle on the 2012 series.
** [[WesternAnimation/TeenageMutantNinjaTurtles1987 The 1987 series]] was a LighterAndSofter show that received a retool late in its run that made the last couple of seasons DarkerAndEdgier. The same thing happened to this show, but in reverse: This was a DarkerAndEdgier show that received a retool late in its run that made the last couple of seasons LighterAndSofter. Also, both retools wound up being very unpopular with their respective audiences.
** Related to that, April gets to meet Usagi in the show's ChristmasEpisode. Creator/VeronicaTaylor would later be cast as an ally to that other [[Anime/SailorMoon Usagi as a fellow Sailor Guardian]].
** Michelangelo is voiced here by Creator/WayneGrayson. Later on, the Turtles meet the Dynamic Duo in ''ComicBook/BatmanTeenageMutantNinjaTurtles''. (granted, the Robin in that series is Damian Wayne, rather than Dick Grayson. Grayson does appear, as Nightwing, in Vol. 2 and as both Robin and later Nightwing in ''Batman/Teenage Mutant Ninja Turtles Adventures'')
** In the ''Fast Forward'' season, one of the Turtles' major enemies is Viral, who, in particular, is often at odds with Donatello due to his role as TheSmartGuy in the group. One year later, [[Creator/SamRiegel Donnie's voice actor]] plays a completely different character named [[Anime/TengenToppaGurrenLagann "Viral" though pronounced "Vee-ral" in that case]]).
** An animated adaptation where a long-running reptilian team is [[spoiler:transformed into dragons]] to tackle a worldwide threat. Are we talking about the "Ninja Tribunal" season or the fourth ''Manga/SgtFrog'' film?
** Mikey is a superhero fanboy who becomes a superhero himself (specifically a BadassNormal in a show full of powered hero, meets numerous superheroes (including Nobody, who bears a superficial resemblance to ComicBook/Batman), and becomes a reserve member of the Justice Force. Fast forward to the Nickelodeon era and the TMNT have crossed over with Batman multiple times.
** Kluh was introduced in the Battle Nexus storyline as a HulkMashUp character and whose name was a SdrawkcabName of "Hulk" in the early 2000s. Many years later, Marvel would actually introduce a villainous Hulk character named "Kluh" who was an intelligent incarnation of Gray Hulk.

!!YMMV for both versions
* CompleteMonster: See [[Monster/TeenageMutantNinjaTurtles here]].

* MoralEventHorizon: See the right section of [[MoralEventHorizon/TeenageMutantNinjaTurtles this page]] for the examples.

* FanNickname: The series is wildly refer as ''TMNT 2003'' or ''[=TMNT2K3=]'' by fans to differentiate it from the [[WesternAnimation/TeenageMutantNinjaTurtles1987 '87 cartoon]].

** Leo is sullen and silent at the beginning of "People's Choice," refusing to join his brothers in exploring the old mill. But when the other three race each other to the roof of the old mill, only to find Leo already up there, ''still'' sullen and silent, and never indicating why he was there at all (he seems to only notice the spacecraft when the others do), it plays off a bit weird. It's hard to tell if it was his way of joining the fun despite his mood, or if something prompted him to climb to the roof separately, or if he was just really determined to force the others to deal with his bad mood.

** In ''I, Monster'', during the end of Leonardo and the Rat King's fight, the Rat King leaped off an unstable piece of flooring which would've soon collapsed into a sea of rats below and landed on Leonardo. Considering how previously, Leonardo had saved him from a collapsing tower, was the Rat King genuinely trying to get away and coincidentally just happened to land on Leo, or was he still acting in a malicious manner and still trying to attack Leo and/or take Leo down with him? Evidently, Leo felt it was the latter, considering he retaliated by angrily kicking the Rat King into the ocean of rats in the lower floor.
** In ''Turtle X-Tinction'', the group sees a clip of a much younger Cody happily interacting with his uncle Darius Dunn... who in the present has already tried to kill him. As the clip is brief and Dunn seems genuinely happy while playfully ruffling Cody’s hair, it’s completely left to the viewer to wonder if there was a time that Dunn ever had any genuine love for his nephew, or was just being nice in a PetTheDog moment (which also raises questions if Dunn treats young children any better than, well, literally anybody else). Could always be a simple case of PragmaticVillainy, though; in that case, being nice was probably in his best interests at that time.
** Did the High Mage genuinely want to help the Underground Mutants and cure their mutations in ''Notes from the Underground, Part 3'', or did he have some ulterior motive? Given that the Underground Mutants are cured ''only'' when they are in the High Mage's city, that he wants his race to be reawakened and retake the world it once ruled[[note]] which further may imply that the Underground Mutants were going to be turned into ''slaves''.[[/note]] and the fact that he's generally a lying prick, it seems that the latter is true, but it still left to the viewer to decide if he genuinely wanted to help them in some manner or not.

* AmericansHateTingle: The series didn't really take off in Japan as well as the [[WesternAnimation/TeenageMutantNinjaTurtles1987 1987 series]] did; the only seasons dubbed were 1 and 2, after which it was cancelled. This also happened to China, Hong Kong and South Korea itself, which also have only the first two seasons dubbed.

** Having an entire six-parter dedicated to a Triceraton invasion of Earth in the ''Space Invaders'' three-parter followed up by yet another ''Worlds Collide'' three-parter where the Triceratons invade Earth, leave Earth, come back again, rinse/repeat, and generally go back-and-forth with the Turtles can be quite tedious to sit through. It all depends on whether or not the viewer thinks this long story arc is worth sitting through for the introduction of Agent Bishop and a few other important plot elements in the Triceraton invasion that would be used for later status-quo-changing story arcs such as Ch'rell utilizing Triceraton technology to escape Earth in the later ''Exodus'' two-parter.
** The ''Search for Splinter'' storyline. While the arc itself — by that name — only lasted two episodes, it was interrupted before reaching a conclusion, by the five episode long ''Turtles in Space'' arc, finally coming to a close at ''Secret Origins, Part 1'', seven episodes after it had begun. Putting one story arc on hold for a while will have that effect.

** The "Midnight Run" song at the beginning of the ''City at War'' trilogy, which expertly captures the light-hearted mood of the brothers enjoying a night on the town while jumping across rooftops.

** Bishop appears to suffer from this in ''Fast Forward'', but redeems himself in ''Day of Awakening''.

** The Demon Shredder is easily the most powerful of the Shredders, or even characters in general, featured in the show, being capable of transforming entire areas to hellish landscapes and summoning legions of undead and demons. His resurrection during the Ninja Tribunal arc was something that inspired fear in even the godly Ninja Tribunal themselves. During his reappearance in ''Tempus Fugit'', he appears to be only as strong as the other Shredders and never utilizes his massive powers.
** Quarry, Stonebiter and Razorfist are intimidating figures and thoughtful fighters for the first episode of ''Notes From the Underground'' and the first few minutes of the second then turn into more passive, easily frightened or defeated characters. This might be justified though given that their leaving their comfort zone to a place that terrifies them, and from what little we see of them in combat against the feral mutants, they are right to be scared since they stand little chance against them.
** Karai gets a spectacular introduction in season 2, soundly defeating the turtles, taking charge of the Foot Clan, and brokering a peace between the warring factions, all while gaining the turtles' trust. Her later appearances have her demoted to one of Shredder's henchmen who struggles to get even a single victory against even one of the turtles. Thankfully this is undone as she takes a greater role in season 4.

** The fight between the Turtles and the Foot Mystics from ''Return to New York, Part 2''. Up to this point, the Turtles have been facing enemies that are largely BadassNormal (Hun for instance) or at least enhanced in some way (ClothesMakeTheSuperman for [[{{Invisibility}} the Foot Tech Ninja]] and GeneticEngineeringIsTheNewNuke for [[GoodAllAlong the Underground Mutants]] for example). In contrast, the Foot Mystics are explicitly stated to be supernatural. Their weird nature was briefly foreshdowed when April mentioned that the floor they are on wasn't listed anywhere, but it still can be a little jarring to some viewers.
*** Their introduction can come across as this, too. The Turtles enter a weird room with some samurai-looking statues... who inexplicably come to life and proceed to attack them. Compared to other enemies, who appeared in previous episodes (the Foot Tech Ninjas appeared first in ''The Way of Invisibility'' and later return in the three-parter), the Foot Mystics never appeared in previous episodes and can feel out-of-place to some.
** Another BLAM happens in ''The Search for Splinter, Part 1''. Raphael isn't able to find any clues on Splinter's whereabouts, he gets angry and decides to stop some crook he saw. This scene isn't plot-relevant at all and it isn't brought up again.

** Leo's character in season 4 where for most of the season he takes on an aggressive take charge attitude in lieu to the fact that he and his family technically lost against C'hell Shredder and Karai in the final battle of season 3 and were only saved thanks to the Ultroms arriving just in time to save them and stop C'hell's plans. Thus he takes any failure in the season pretty hard and lashes out ("Dragon's Rising" in particular where he chews out his brothers and Casey just because they only stopped ''half'' of the weapons cargo the Purple Dragons had stolen rather then all). On one hand, most did like that it was part of his character development in eventually learning it's okay to fail if you give it your all long as your survive and learn from it. But others fans likewise hated that they had to wait for most of the season for it and had to put up Leo's demeanor in the meantime, making it hard to watch since he was always angry and feeling TheReasonYouSuckSpeech was unwarranted since they did ''try'' their hardest (not helped with Ralph ''agreeing'' with him). Though ironically this was foreshadowing to the lesson Leo needed to learn later on.

** A unique example took place in the Season 6 episode "The Journal". Due to the fifth season being put on hold so the sixth could air first, first-time viewers were caught off-guard when the episode depicted characters and settings that had only been introduced in the fifth season. [[spoiler:Nano is seen as a member of the Justice Force, and the Ninja Tribunal are seen outside of their distinctive Shredder armor, when they had not been unmasked by the Season 4 finale in which they'd last appeared. Karai's apparent HeelFaceTurn is less obtrusive since the journal's contents were fabricated, but it still might tip off a viewer that Karai ends Season 5 on an ambiguous note.]] The appearance of a Foot Mystic also took viewers off guard given their last scene in "Good Genes, Part 2", but at least that is explained as [[spoiler:Splinter simply chucking them into the story at random.]]
* DracoInLeatherPants: Agent Bishop gets this treatment from a large portion of the fanbase. While he does change his ways and brings peace and stability to the Earth in ''Fast Forward'', he still committed a lot of evil deeds in the bulk of his appearances, most notably attempting to dissect the Turtles and Splinter multiple times, torturing Leatherhead, ruining the lives of his own men by mutating them into monsters, and torturing countless sentient alien beings in the decades leading up to his ultimate HeelFaceTurn. Even though there's little doubt that Agent Bishop is a complex character and multi-faceted AntiVillain who himself was experimented on by aliens during the Civil War and thus, has a [[FreudianExcuse sympathetic and believable motive]] for wanting to keep Earth safe from aliens invasions, a lot of his fans still have a tendency to play down all his evil deeds and romanticize him as little more than a noble and selfless HeroAntagonist who only has the best interests of the world at heart, even though many of his pre-Fast Forward actions show that he's NOT(most notably when he openly admitted to Splinter in "Bishop's Gambit" that he honestly doesn't care if innocent people get killed by his Slayers in his quest to root out aliens). What also helps his case is that Bishop tends to be given a free pass by many fans for acts that they would crucify other villains for. When Karai tried to kill the Turtles and Splinter in ''Scion of The Shredder'' in an assault on their home, fans were about ready to lynch her. However, when Bishop did something similar in ''Bishop's Gambit'' by forcing the Turtles out of their homes with sonics, kidnapping Splinter, and trying to have the Turtles killed, fan reactions to his ruthless actions were much more muted, if not totally silent, by comparison.

** Hun and Bishop, to the point of becoming [[CanonImmigrant Canon Immigrants.]]

** Traximus, the triceraton gladiator who becomes FireForgedFriends with the heroes and the RebelLeader against his oppressive government, is seen as a highlight of the three arcs he appears in.

** In a Meta sense, this version of April is generally better liked than the other versions that aren't Channel 6 reporters.

** Agent Bishop, the most iconic character created for the series and for good reason. He’s well-regarded for being brilliant, crafty, and genuinely dangerous in direct combat. His interesting backstory made him stand out amongst the series’s villains as well.

* FanNickname: The series is wildly refer as ''TMNT 2003'' or ''[=TMNT2K3=]'' by fans to differentiate it from the [[WesternAnimation/TeenageMutantNinjaTurtles1987 TMNT '87 cartoon]].
* FanficFuel: The BadFuture shown in ''Same As It Never Was'' invites a lot of speculation for fans. How exactly did it come about? Where are the characters we do not see, if not dead, and what are they doing? How exactly were [[spoiler:Splinter and Casey killed]]? Why did Donatello disappear and how did his family and friends handle it?

** Some fans have speculated that the villain Khan from the seventh and final season of the show was actually one of the four Foot Elite who were relatively prominent supporting villains from the first five seasons due to sharing the same leitmotif as them.
** Leonardo is widely believed to be blind in the BadFuture shown in ''Same As It Never Was'', to the point where many assume it's canon, though WordOfGod says that wasn't the intention (but didn't outright [[{{Jossed}} joss]] it).
** Some have theorized that the human looking characters seen in the ''Turtles In Space'' and Triceraton Invasion arcs are actually humans from Earth abducted by aliens or descendants of them. This is helped a bit by the alliance formed by General Blanque and Agent Bishop as [[spoiler: Bishop himself was abducted by aliens in the 1800s]].

** In "Mission of Gravity", Karai defends her decision to continue serving the Shredder by asking Leo if he could so easily turn on his father, even knowing he was evil. Four episodes later in "Reality Check", the audience is shown an alternate universe where Splinter is a villain opposed by the still heroic Turtles.
** Leonardo accidentally stabs Splinter in his nightmare in "The Darkness Within". Come "The Ancient One", he ends up ''actually'' injuring Splinter after losing his temper.

** In "Hunted", Leatherhead shows deep care for Michelangelo when he accidentally hurts him [[spoiler: and is extremely happy when he Michelangelo alive and well]]. Fast forward to [[WesternAnimation/TeenageMutantNinjaTurtles2012 the 2012 series]], where the two become best friends.
** In "Tale of Master Yoshi", Leo spoke fondly of Tang Shen, since he states Yoshi's story is about "a girl". Come ComicBook/TeenageMutantNinjaTurtlesIDW and you see [[spoiler:Shen and Leo being mother and son respectively, especially when the former comforts her older son in spirit.]]

** In "Shredder Strikes Back: Part II", Raph flashes back to the Shredder's (first) defeat, and states that "Nothing Human could have survived that!" Much later, it would be revealed that the Shredder ''isn't'' human.
** In "Exodus", it was promised "[[WhamEpisode One of these characters will never be seen again.]]", and after the episode, Ch'rell is banished to an ice planet, likely never to be seen again... That is, until ''WesternAnimation/TurtlesForever'', but even before that, Peter Laird confirmed that the Triceraton Shredder shown in concept art of a possible second ''Fast Forward'' season would have been Ch'rell hijacking the body of a Triceraton soldier, and ''Back to the Sewers'' not-so-subtly implied in its first episode that Ch'rell would fight the other two Shredders in the show (there would have been an arc called "The Shredder Wars"). Making the claim that Ch'rell would never be seen again ''hysterical''.
** On a similar note, there's this exchange, from season 5, before the Cyber Shredder was introduced (and, consequentially, before ''WesternAnimation/TurtlesForever'' and the whole 'Multiverse' thing).
--->'''Mikey:''' 'Real Shredder', 'True Shredder', 'Utrom Shredder'...

** Early on in season 1-- the episode "The Garbageman"-- Mikey tries out several catchphrases, much to his brothers' distaste. One of those catchphrases is "It's trench-coat wearing time!". Nobody (except the fans) seems to have a problem with "It's ''ninja'' time" five seasons later.

** In the ''Fast Forward'' season, one of the Turtles' major enemies is Viral, who in particular is often at odds with Donatello due to his role as TheSmartGuy in the group. One year later, [[Creator/SamRiegel Donnie's voice actor]] plays a completely different character named [[Anime/TengenToppaGurrenLagann "Viral" though pronounced "Vee-ral" in that case]]).

** Baxter Stockman in the episode "Insane in the Membrane". Sure, he was an arrogant jerk, but we learn that he used to be a very sweet kid and in the present day breaks down after seeing hallucinations of his dead mother, which is made worse by his regret of never fulfilling his mother's dreams for her son while she was alive. It's especially hard to not feel sorry for him after he ends up dying after his new body completely decays and Bishop resurrects him, denying him a chance at finally dying in peace.

* MemeticMolester: The alien frog from the ''[[Recap/TeenageMutantNinjaTurtles2003S6E12BadBlood Bad Blood]]'' episode. From his tone of voice and the way he grabbed Cody makes him look like a child predator.

** The family-friendly swearing by having the turtles say "what the shell?" rather than hell can get a little silly sometimes, especially in otherwise serious moments.
** Leo is sullen and silent at the beginning of ''People's Choice'', refusing to join his brothers in exploring the old mill. But when the other three race each other to the roof of the old mill, only to find Leo already up there, ''still'' sullen and silent, and never indicating why he was there at all (he seems to only notice the spacecraft when the others do), it plays off a bit weird. It's hard to tell if it was his way of joining the fun despite his mood, or if something prompted him to climb to the roof separately, or if he was just really determined to force the others to deal with his bad mood.
** Season four's "Scion of the Shredder" features Karai responding to the foot soldiers under her command with "excellent" three times in a row in the span of a few minutes. It's easy to be reminded of Mr. Burns from the Simpsons and runs the risk of undermining a very dramatic sequence.
** Leo's reunions with his brothers and Splinter in ''Prodigal Son'' are mostly quite sweet, but when he finds Don and Splinter, Don runs joyfully to him and they... shake hands. Not that the brothers are big "huggers" in general, but Don ''has'' hugged Raph and Mikey, Leo can usually at least manage an affectionate shoulder-pat with his brothers, they hadn't seen each other for ages, and neither of them knew if they ever ''would'' see each other alive again. Given the moment, greeting with a handshake came across as awkward and formal.
** Some of the recycled animation can take a viewer out of it at times. For example, the Utroms coming to the rescue in “Exodus, Part 2” is lifted wholesale from “Secret Origins, Part 1”, but with new dialogue dubbed over.

** While the "Fast Forward" season was maligned for many reasons, a substantial amount of the blame is still heaped upon [[CousinOliver Cody Jones]], due to how he was basically TheLoad added to the existing team dynamic of the turtles and Splinter, with most of the ''Fast Forward'' episodes based around him being a turtles fanboy and his uncle conspiring against him. He got more competent later in the season, but this lead to people having the opposite complaints—Cody became the one who ended up saving the day more often then not (especially in "Day of Awakening") which got him labelled as a CreatorsPet to some extent.

** The 7th and final season, ''Back to the Sewers'' got even worse reception. Despite returning the show back to its present-day roots and bringing April and Casey back into the picture, it adopted a new art style [[TheyChangedItNowItSucks that turned off many viewers]], an unpopular focus on the Turtles going into cyberspace, and whatever seriousness that was still left over in the show from ''Fast Forward'' was thrown out altogether to make the show [[DenserAndWackier even goofier]].

** Mr. Touch and Mr. Go might have made nice additions to Hun's revamped Purple Dragons and help transition it for a street gang to something more organized but are never seen again in that seen again. Likewise, it would have been interesting to see the more notable and long-lasting Purple Dragons goons who'd been with Hun for so long transitioning into the roles of more hi-tech, heist oriented criminals throughout those episodes.

** In season 3, the Turtles existence is revealed to the world's leaders by [[AlienInvasion the Triceratons]] when Zanramon displays a captured Donnie to the world. Nothing ever comes of this, though the Earth was rather preoccupied with a hostile alien invasion of the planet and the recovery thereafter. The idea is touched upon again in “Aliens Among Us” when during the President’s press conference, an artist’s impression of what was likely his fearful description of the Turtles is displayed, but nothing comes of this either and it’s played as more of a gag anyway. Neither situation really came off as a public outing of the Turtles like in the spiritual attack in “Bad Day”, so it’s not unreasonable that the show was not changed by either of these events.

** Beijing, the capital city of a superpower, spends several episodes floating in the air due to a gravity device that the Triceratons deploy during their invasion. The implications of this (what effect if any it has on the Chinese government structure, how the people in the isolated city view their predicament, how they feed themselves, etc.) had a lot of story potential. However, nothing about the people and society of the city are explained when the Turtles and the Foot Clan go to Beijing in ''Mission of Gravity'' and bring it back down to Earth.

* UnintentionalPeriodPiece: The show manages to be fairly timeless if obviously set in the very early 21st century. Occasionally some dated technology references pop up; in "Trouble with Augie", April’s sister Robin asks to use her desktop computer to check her email, when by the 2010’s anybody can check their email on their smartphone.

** Though not popular, Serling is probably one of the biggest woobies. Most, if not all the fans hate him and in-universe, the other characters treat him like a slave sans Splinter and Cody, suffers bad luck which is sometimes caused by his buttmonkey status, while other times, his pain and suffering is deliberately caused by the turtles (i.e. trapping him inside a video game surronded by extra lives that look and act like the turtles). Honestly, it's a miracle he never tried to commit robot suicide.

** Razorfist from the ''Notes From The Underground'' stage. he blocks your attacks from the front, so logically that means that you should attack him from the back right? Unfortunately he's aware of that and uses a backslam against you if you linger too long from the back. His other attack is a high speed charge around the area that's hard to dodge.
** King Nail also from ''Notes From The Underground'' for everyone except Mikey. He hits hard and mostly spends his time in the air flying around the room making it hard to hit him. Michelangelo doesn't have that problem since his jump attack temporarily allows him to glide in the air and hit him more frequently and avoid some of his attacks.

!! YMMV for the Video Game Adaptations

** [[TrueFinalBoss Oroku Saki]]. He's only fought after you beat Shredder with all four turtles and is suppose to be the toughest challenge. Unfortunately you've already gotten the CombinationAttack allowing you to damage him for a good amount of health with three button uses. So it's only a matter of wittling away the rest.
** The BadFuture Mega Shredder gets billing in the opening cutscene of ''Mutant Nightmare'', building him up as a threatening late-game boss fight. However, the fight itself is given comparatively little fanfare, his attacks are rather basic considering his intimidating design, and the laser cannon placed in the arena to [[BossArenaIdiocy let the player disable Mega Shredder and his damage-preventing shield]] practically trivializes the fight.
** Felkyrie in ''Mutant Nightmare'', found at the end of the BossRush that is Leo's Nightmare. Despite the game having voice lines talking about how threatening it is and a warning message about its invulnerability, it has a very obvious window of vulnerability after its strongest attack. It also attacks somewhat infrequently and its attacks are fairly predictable, meaning that it tends to go down very quickly once you figure out its patterns.
* DemonicSpiders: Blaster-wielding Federation soldiers in ''Battle Nexus''. Unlike most enemies that use lasers, who tend to fire one shot at a time or in short bursts, these guys go ''[[BeamSpam full-auto]]'' when they line up a shot, and getting hit even once will electrocute you and leave you vulnerable to follow-up attacks from them or any other enemy. They can very easily trap you in a CycleOfHurting that takes away a good chunk of your health if you're not careful, especially when more than one shows up at a time.
* DifficultySpike: The third stage in ''Battle Nexus'', Planet Zero, is much more difficult than the earlier stages with tougher enemies and tricky platforming. The game just keeps getting harder from there.
* EnsembleDarkhorse: Slashuur, the [[CanonForeigner original]] RecurringBoss and a SecretCharacter in ''Battle Nexus'', due to his cool design, NobleDemon characterization, and being a GoodCounterpart to The Shredder. Some fans wished that he [[CanonImmigrant became canon]] to the 2003 series, or at least hope that another incarnation will adapt the character.
* GameBreaker: The CombinationAttack in the first game. You get it after beating the Ordeal stage with all four turtles. It's activated by a simple push of a button. It's drawback is that can only be used in the Story Mode 3 times in a level but all 3 uses can take a huge chunk of health from every boss. Even [[TrueFinalBoss Oroku Saki]] himself.
* GoddamnedBats: Play the latter two games enough and you ''will'' learn to hate Foot archers. ''Battle Nexus'' has a particularly horrid tendency of [[LedgeBats putting them in the middle of platforming sections so that they can take potshots at you while you try to jump over pits]], while the ones in ''Mutant Nightmare'' almost always come packing flaming arrows that explode in a small radius and knock you down.
* SugarWiki/NoProblemWithLicensedGames: The first and second games (''Battle Nexus'') based on this series have a cult following, the latter especially thanks to its' challenging enemies, lengthy campaign, lots of replay value, tournament mode, and inclusion of the original arcade game. The third game was not ''quite'' as well received but still has something of a following.

** Slashuur in ''Battle Nexus'' is known for being an absolutely horrid brick wall even by WakeUpCallBoss standards. With aggressive AI, fast attacks, a long weapon reach, projectile immunity, teleporting whenever you hit him, and the ability to heal when he hits you, Slashuur is capable of punishing mistakes ruthlessly while regaining health, resulting in the player suffering a protracted DeathOfAThousandCuts if they're not an expert in the game's combat system. The fight basically runs on UnstableEquilibrium: if you're good at the game, his low health means he won't last long, but if your reflexes aren't up to scratch he's essentially invincible.
** In ''Mutant Nightmare'', both of the bosses in Mikey's Nightmare. They also happen to be fought using laser cannon and shuriken controls respectively, meaning that the bonuses you built up over the game won't help you:
*** Tostegaron is a LevelInBossClothing fought using laser cannons that has to be chased and fought three separate times before he goes down. The first two encounters aren't too bad - just make sure you're shooting his boulders down and shooting him to interrupt his thunderclap. The third one, however, is where it gets really messy; he will constantly use his thunderclap attack while enemies constantly spawn to harass you and divert your attention. If you don't focus down Tostegaron, he will TotalPartyKill you. If you do focus him, that gives the enemies a chance to wear down your team and maybe kill one or two turtles, and then you won't have enough damage to interrupt and finish off Tostegaron, and ''then'' he'll TPK you. It really doesn't help that [[ArtificialStupidity the allied AI can never seem to decide what they want to focus on, and don't attempt to interrupt Tostegaron nearly as much as they should]].
*** The Sliver [[TimeLimitBoss has to be defeated in a very strict 2 minutes and 30 seconds]], and is very good at stalling out the timer. You fight him using shuriken, which have a travel time, and [[GetBackHereBoss he never holds still]]. His attacks include a punch that inflicts a lengthy stun if not blocked and an energy ball that traps your team in a cage that has to be broken if it connects; every punch and energy ball that connects will waste your precious time, and as per usual, ArtificialStupidity means that they connect far more than they should. And that's not to mention his team-hitting lightning, which the AI once again fails to block consistently (and can't be blocked at all if he stunned you with a punch beforehand), and losing a turtle is almost guaranteed to make you lose the fight by making the energy balls and cages take that much longer to break.
* TheyWastedAPerfectlyGoodPlot: To this day, avid fans of the Konami games lament that the series ended and never had the chance to adapt the remaining seasons.

** While the sentiment isn't totally universal, the ''Fast Forward'' sixth season in this day and age is a little better regarded than what it used to be back in the day. At the very least, it's seen as having an interesting if flawed concept that didn't fully get to grow and blossom, especially with regards to Space Usagi, the [=TriShreddatron=], Leatherhead coming back, and the Dark Turtles making a full HeelFaceTurn in the unproduced ''FF'' episodes. And there were at least a few character from this season who became popular enough that fans would like to see them in future installments such as Viral and the Dark Turtles or who ''did'' appear in future installment like the IDW series (ie: Dunn, Jammerhead, Torbin Zixx). While very few people would list ''Fast Forward'' in their top five list of Ninja Turtle stories or installments, the season these days is being judged a little more fairly and enjoyed on its own merits rather than being compared to the previous Mirage-inspired seasons. And to really put things into perspective, even up to today, practically nobody is clamoring for ''Back to the Sewers'' characters like Khan or the Green Mantle to make any sort of comeback and those characters have largely faded into obscurity, whereas now fans are much more open to ''Fast Forward'' characters and concepts making their way into future TMNT media and ComicBook/TeenageMutantNinjaTurtlesIDW has given a chance for some of those characters to have a second go in a new medium.

* CatharsisFactor: "Exodus, Part 2" ends with a triumphant, powerful victory for the Turtles. [[spoiler:The Utroms arrive in time to save them and Splinter from their HeroicSacrifice and immediately capture the Shredder. The Turtles receive desperately needed medical attention, Honeycutt is given a new body, and this time, Shredder does ''not'' escape his confinement. What follows is a brutal trial of the Shredder in which his war crimes and ''millions'' of innocent victims are laid bare, and earn him a life sentence of exile to a distant asteroid without any means of escape (and as ''Turtles Forever'' would later show, resulted in him freezing solid unable to leave). It's so damn ''satisfying'' to finally see the Shredder brought to justice, and until ''Turtles Forever'', it ''stays'' that way.]]

* VindicatedByHistory: While the viewpoint still remains far from universal, the reception to Shredder being an Utrom has improved with the passage of time. As the reveal elevated the villain's potential from a human criminal mastermind with an army of ninjas to a cosmic-level threat capable of bringing the universe to its knees. In particular, it's not uncommon to note that Ch'rell is almost an amalgamation of Shredder's skill and strength as a Ninja combined with the intelligence of a much more sadistic Krang. Also with how ridiculous the TMNT franchise has become across its various incarnations, the idea of Shredder being an alien is simply no longer as unusual as it once was. Even those who still aren't fans of the idea will admit that, looking back, this version of the Shredder still has a lot of other traits they want to see out of the character.

** Torbin Zixx from ''Fast Forward'' tends to be rather disliked by fans due to all three of his appearances largely boiling down to conning or swindling the Turtles, and having little-to-no redeeming qualities.

** ''Fast Forward'' shifted the Turtles to the future and went for a more [[LighterAndSofter lighthearted]] tone, which alienated fans who preferred the darker prior seasons, but the season often referenced plot points and characters from prior seasons who understandably [[PutOnABus weren't present]] due to the shift in setting (or in the case of Bishop and Baxter, were present), which left it [[ContinuityLockout difficult]] for newer fans to get into.
** ''Back to the Sewers'' brought the Turtles back to the present day, pitting them against the Foot Clan, Purple Dragons, and some of their other rogues again, seemingly an attempt to [[PanderingToTheBase win back prior fans]], but retained the light-hearted tone of ''Fast Forward'' as well as became [[DenserAndWackier goofier]], while also downplaying the series' previously strong continuity, likely to [[SoftReboot serve as a jumping on point]] for new fans. The result is that it wasn't very appealing to the established fanbase of the series for the change to the series' serialization, nor very appealing to potential new viewers who didn't follow the prior seasons.