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: Teenage Mutant Ninja Turtles 2003
Badass Decay: Bishop appears to suffer from this in Fast Forward, but redeems himself in "Day of Awakening".
Fridge Brilliance: After his defeat in "The Shredder Strikes, Part 2," Shredder makes it a point of going after the Turtles and eliminating them. Seems like common sense and simple revenge, right? But then "Timing is Everything" showed Shredder after his first defeat facing the more-skilled Turtles by way of time travel. He knew they would become more powerful and eventually defeat him (as Raph says), so his motives weren't pure revenge.
Fridge Horror: Possibly mixed with Harsher in Hindsight. An un-produced episode of the Ninja Tribunal season was going to reveal that Hun and The Garbageman were conjoined twins separated at birth by a back-alley surgeon. That was horrific enough that it got the episode scraped by the network, but it gets even worse when who realize that it was hinted at two seasons earlier during "Same As It Never Was." Brings the Shredder's punishment of Hun and Stockman to an all-new level of "apropos."
In "Exodus", it was promised "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 Turtles Forever, 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 Turtles Forever and the whole 'Multiverse' thing).
The Fast Forward season with the turtles living among aliens could count as this, considering Michael Bay's announcement that the turtles will be aliens in his film.
Not so much now since it has recently been confirmed that nothing about the turtles has changed and Bay isn't really in charge of the film's development other than financing it.
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.
Magnificent Bastards: The Ninja Tribunal. Can also be considered Guile Heroes since they are on the Turtles' side. Plus, the fact that they plan for the turtles to meet their destinies whether they are able to defeat the Demon Shredder or not is considered GOOD magnificent bastardom indeed.
The Heralds of the Shredder, a.k.a. the Foot Mystics, count as well for two of their successful plans; one to have Bishop free them by destroying the Heart of Tengu that allowed its user to control them, and the next one to resurrect their true master, the Demon Shredder, despite the failures of their demonic mooks.
Moral Event Horizon: For the Shredder, this was the episode "Mission of Gravity", where we learned that not only is he willing to kill millions when it serves his purposes, he'd also do so when it wouldn't.
Nightmare Fuel: Baxter Stockman, especially the episode "Insane In The Membrane".
Shredder's reaction to Stockman's continued failures.
Same As It Never Was, the episode seemed to have been intentionally designed to be utterly terrifying, and probably to show exactly what the Shredder would do if he were to take over a planet, the results are, yet again, terrifying.
The Shredder trapping the Turtles, Splinter, Casey, and April in April's antique shop closet by setting the place on fire using the gas pipes. It set up a big two-part episode cliff-hanger for the show, which no doubt scared a lot of kids back in the day.
The Utrom Shredder and Stockman are hated for repeatedly cheating death. In the former's case, the biggest offender was surviving the TCRI explosion (albeit, it did injure him enough to the point he needed some time to recover) and the latter for being flat out arrogant, seeing the mutants in the show as "stupid animals", even though 2 of those stupid animals (Donatello and Leatherhead) are more intelligent than him and just acting condescending to anyone he deems to be intellectually inferior.
Starlee's family is rather annoying. Her mother is snobby and thinks of her species and planet as above others and acts rather rudely (she thinks Donatello is a criminal for wearing a mask, and asks if he's had his vaccination shots when he knocks everyone down to avoid getting hit by a laser). Her little brother, also messes with things he's not supposed to touch and gets away with it apart from Starlee yelling at him. It's not much of a surprise to see why Starlee didn't want everyone to meet her family.
Seasonal Rot: By Fast Forward, although some people would place it even earlier.
Really Season 4 was the high point with some complex and surprisingly well written arcs for both Leonardy and Michelangelo. The two retools made the show much more child friendly and typical (robots, digital realms, collect the clues saga), but Season 4 stands as a nice end to a good cartoon.
A few fans stopped watching the show when it was revealed that the Shredder was an Utrom.
Strawman Has a Point: Throughtout Season 4, Leonardo becomes increasingly hardened and more of a jerk than Raphael ever was. After the Turtles and Casey fail to stop a Purple Dragon convoy in "Dragons Rising," the trope is invoked as Leonardo delivers a pretty brutal "The Reason You Suck" Speech:
Leonardo: Half! We stopped half and only because we got lucky! Is that good enough for you? Is it?! We're always one step behind! We act like a bunch of amateurs! How many times are we gonna get beaten before you guys wise up and realize this isn't a game?! (storms off) Raphael: I hate to admit it, but he ain't wrong.
Tear Jerker: A few episodes. Especially any episodes involving Nano.
Kirby giving Donatello a sketch of him with a ray gun and final words: Don - "Life at best is bitter sweet." Take care of yourself. - Kirby
The entire 2003 series got accused of this by fans of the '80s cartoon, with complaints that they wished it was more like the "original" series. The irony being that the 2003 series, was far more faithful to the REAL original Turtles of the comics, than the '80s series ever was. It was hit with this even more in Japan, where they were more fond of the 1987 Turtles.
They Wasted A Perfectly Good Character: Or characters, in this case The Dark Turtles. Mostly due to their subplot being dropped to make way for Back to the Sewer. Dark Leo's time with the turtles in their final appearance suggested the four had a chance to turn good at some point, but this would never come to pass.
Villain Decay: Inverted, the Shredder managed to stay a dangerous antagonist, he even managed to top himself in every evil plan he committed, with the Utrom Shredder being considered the most dangerous of the bunch.
Hun himself though, seems to play it mostly straight, while he can fight the Turtles, he gets significantly more pathetic, while later seasons do try to avoid it, he ends up becoming a bigger loser, though, to be fair, in Back To The Sewers, he learned more techniques that allow him to fight the Turtles and even becomes a Crime lord... Doesn't stop them from learning to fight him again, although in Turtles Forever, he turns into a Turtle Monster, he ends up being so powerful that the Turtles can't lay a scratch on him.
Karai suffers this badly in season 4. From one appearance to the next, she goes from destroying the turtle's lair, all of their vehicles, and nearly killing 3 out 4 turtles and Splinter to playing and losing a rather humiliating game of keep away for a McGuffin against Leo and Mikey, including a sequence where they pick her up and drag her by the legs before throwing her out of an elevator shaft, in a manner more suiting Bebob and Rocksteady.
The Cyber Shredder, granted, it's the Shredder's data before Shredder became more and more Genre Savvy, but... His plans constantly fail and get repetitive, even when he does get out of Cyberspace.
Villain Sue: Bishop, due to the sheer ease that he manages to outfight the Turtles, Hun & Karai, his repeated elaborate escapes & the fact that even when he loses, he still wins in the grand scheme of things.
You aren't, this Troper still cries in Nano's appearances.
To recap, in Nano's first appearance, it's defeated by getting dropped into a vat of molten steel, and survived, and only to get broken into pieces when returned. An AI that's only a child at heart and doesn't fully understand right from wrong gets defeats more painful that what the villains in the series endure.
Nano's father figure Harry the Pick-Pocket is also a little bit sympathetic. True, he mainly went along with Nano's delusions that he was its father so it could help him in his crimes, but at times he acted as if he actually cared about Nano. This is made especially apparent when he mourned Nano's demise in its debut episode and was overjoyed to see it alive and well in its second appearance.
And let's not forget poor Dr. Stockman. This Troper has never felt so bad for a villain until "Adventures in Turtle-Sitting", in which , after being revived again, asks why Bishop doesn't let him rest in peace.
Donatello, arguably, he's dealt with some of the worst crap in this series, he's been in a Lotus-Eater Machine where he's seen Angel die before his eyes, another where he's in a bad future, where he sees all of his brothers and learning all of his best friends have died, and was turned into a beast, at one point, life is rough on him.
Though not popular, Sterling 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.