Alternative Character Interpretation: Fred Wolf Series: This theory seems to have arisen for some... is Irma chasing after guys really her desperation in nabbing herself a man, or, is it an act of desperation to cover up her being a closeted lesbian?
Base-Breaking Character: Venus de Milo. Most fans see her as a Replacement Scrappy for April O'Neil, but some fans think that she is an interesting concept and would like to see her return in one of the current Nickelodeon-helmed adaptations. It's particularly telling that even the franchise's creators have differing opinions on her: While Peter Laird is well-known for outright despising the character, Kevin Eastman has gone on record to say that he likes the character and hopes for her to someday make a comeback.
Better Than Canon: Some fans, who do like Venus de Milo, tend to make her more well written, give her flaws and a different backstory.
Some works. But nearly everyone tries to forget Next Mutation.
How most fans of the 80's series treat the Red Sky seasons (though some are fond of season eight).
Funny Moments: In the 2007 movie, Splinter talking about his "stories", especially him muttering to himself about how "Cody is going to break up with Donna, I just know it."
Genius Bonus/Shown Their Work: In the 80's cartoon, the main reason for Baxter Stockman becoming more and more absent minded after his mutation as the show went on wasn't because of Flanderization, but because flies have poor memories and can be very scatterbrained in real life.
Moral Event Horizon: Shredder officially crossed this in the opening episode "Get Shredder" where he actually destroys the Channel 6 building which takes it out of commission for the rest of the series.
In the episode "Splinter No More", it's pretty hard to see Splinter lamenting his loss of his humanity to the point of shedding tears. This becomes much Harsher in Hindsight when you remember that Splinter destroyed Shredder's Retro Mutagen Ray in order to save the turtles, but also destroying the one thing that could return him to his human form in the process.
Also in the episode "Hot Rodding Teenagers", it's tough to see Kala break down as she explains that the only reason that she and the other Neutrinos are on the run is because that they are kids who would like to have fun instead of fighting in Dimension X's infinite war, and are being hunted down for it.
The penultimate example for most fans of the original series is in the opening episode "Get Shredder" where Shredder actually destroys the Channel 6 building which takes it out of commission for the rest of the series.
Fans of the original Mirage Comics dish on the Fred Wolf show for "selling out". Fans of the Fred Wolf show say this about the 4Kids version and its more serious tone. Fans of the first five seasons of the 4Kids show will scream obscenities at Fast Forward due to its radical shift in tone, setting, and look. This was Lampshaded in Turtles Forever when the Fred Wolf turtles and 4Kids turtles arrive in the 1984 (Mirage) universe. The original turtles there call the others 'sell outs' though they eventually settle their differences.
The 2012 cartoon has suffered this from fans of both the 80's and 2003 version.
Uncanny Valley: Usually a problem with the turtles in Live Action Adaptations, most notably the cheap Coming Out of their Shells Tour and We Wish You A Turtles Christmas Special. Splinter often looks even worse.
The 2007 CGI movie, on the other hand, makes the turtles look quite nice, but the human models have been accused of this.
The costumes in the Operation Blue Line promotional video — which was about a light rail service that went from Los Angeles to Long Beach, and released only in California for free — blow everything else out of the water. 
"Weird Al" Effect: The original comic is a spot on pastiche of Frank Miller's work circa the early to mid 80s (mostly Ronin and Daredevil); the writers being big fans. The best example is The Foot, who are based on Marvel's The Hand (get it?).
Also compared Daredevil's master (Stick) to the Turtle's master (Splinter). Both origins involve a truck of toxic waste too. The first issue starts with a page-by-page rip off of the toxic accident that created Daredevil, up to and including the "kid saving an old man and getting blinded" bit. If it weren't for their divergent timelines or the copyright being owned by different companies, the idea was that the blind kid is Daredevil and the canister that created him also created the Turtles. Marvel actually did have the rights to the Turtles comics at one point, but they were set in a separate universe, so perhaps the Turtles are part of the Marvel multiverse and in this one, Matt Murdock never became Daredevil and just became a blind kid.
A few elements were cribbed from X-Men as well; Leonardo was Cyclops and Raphael was Wolverine; and when Krang and Shredder◊ appear together, they seem eerily similar to Mojo and Spiral◊. While the X-Men have gone onto prominence in their own right, for a while they were less known to the public than the Turtles.
The Neutrinos in their debut episode count for this considering that they were being hunted in their home Dimension X just because they actually opposed fighting in the never ending war happening there.
Kala: "You don't know what it's like.... living in a place where everyone wants to do you in....just for the crime of being young." (She starts to cry.)
And like his mistress, Kala's pet Grybyx falls under this category in his debut episode.
Tropes that pertain to the 1989 Nintendo Entertainment System video game:
Anticlimax Boss: After all the crap it takes to reach him, Shredder is a relative pushover due to the fact that he's the only boss in the game that can be knocked back. Players who get him in the right rhythm can just keep smacking him without giving him a chance to counter.
Breather Boss: The Big Mouser at the end of level 4. It's completely stationary, and its only attacks are occasionally firing an eye laser and dropping regular mousers. If you stand under it with Donatello and spam your upwards attack at its weak point, neither of these will ever hit you.
Demonic Spiders: It's bad enough that there are respawning enemies but there are some enemies that really make this game unfair and annoying to play.
The worst enemy that you will encounter in the game are the Flying Spacemen armed with laser guns in the later sections of the Technodrome. They appear and move so quickly that you almost can't react to them without getting hit. What's even worse is that there are sections of narrow halls that make getting shot or running into them an inevitability. It also takes two shots from the Scroll, the best sub-weapon in the game, to kill them.
The spider robots in Area 5 are notorious for making climbing sections a total pain since they move fast towards you and you're completely defenseless while climbing the wall.
The large porcupines in the underground sections of Area 5 are cheap and unpredictable as they jump and attack in completely random patterns, making it hard to not get hit by them.
Ear Worm: The overworld music for Stages 1 through 5, building theme 1 and the boss music are popular choices.
Game Breaker: The scroll weapon makes quick work on most bosses. However, it's extremely rare and can be replaced by other subweapons.
Also Donatello, considering that his bo staff had absolutely absurd offensive power and range, which made most boss fights pretty trivial.
Good Bad Bug: The North American MS-DOS version has a required jump that is literally impossible to accomplish. However, you can still beat the game without cheats, if you do a sequence of extremely strange actions (although you still skip the rest of that level). If you have rope, there's a place on the overworld that you can walk, which triggers the use of the rope. Suddenly, you're using the climbing animation on the overworld. If you now enter a specific building, you will fall through the floor into a glitched level. You might end up dead, or the game asking you to insert another disk, or just trapped in a broken level, but there is a chance that the game will instead teleport you to the beginning of the next level. 
Porting Disaster: The North American PC version to say the least. The third stage cannot be completed without cheating or a very strange glitch because of a design flaw in one of the sections in the sewers. The jump is impossible to make because of the ceiling being shorter and the platform on the other side missing a block. The UK Teenage Mutant Hero Turtles corrected this by extending the platform, but retained the other design decisions that made many aspects unintentionally more difficult.
The first few seconds of the intro music sounds incredibly similar to "Stone Cold Crazy" by Queen.
The Area 5 overworld theme resembles the opening riff of The Beatles' "Come Together".
That One Boss: The Technodrome boss in level 5. First of all, level 5 is a Scrappy Level in itself due to the fact that the boss is randomly placed at the end of one of three caves. As for the Technodrome itself, the prong in its front fires a powerful lightning beam that covers a third of the play area, making it nigh impossible to approach without using secondary weapons to destroy said prongnote or exploiting a glitch with the pause menu that makes the bottom half of the beam disappear. On top of that, it also has two turrets on the body firing a constant stream of bullets at you, as well as the open compartment at the top which spawns infinite Foot Soldiers to further hinder you. All of these have to be taken out if you want any chance of safely attacking the eye at the top, which is the boss's true weak point. Hope you packed a lunch!
That One Level: The notorious dam level, dubbed "That Damn Dam" by some, and some fan theories persist that this level was what turned famed movie critic Roger Ebert off of video games (he played to this level, which allowed him to spot an inaccuracy in The Wizard.) The dam level owes its infamy to the following factors...
It's a Timed Mission. You are charged with defusing eight bombs under a time limit, with annoying sea life everywhere trying to inhibit your progress. Failing to defuse them all before time runs out will result in a...
Non Standard Game Over. It doesn't matter how many turtles you have left; you fail once, and it's all over. Luckily it's the only game over of its kind in this game, since according to gamers who managed to pass this level, the game gets even harder.
Tier-Induced Scrappy: Raphael, oh dear god Raphael. The main reason for this is because instead of thrusting his sai daggers forward like he should, he just sticks out his arm and spins them in place which means he has absolutely no range on his attacks as opposed to the other turtles who actually have decent range with their attacks.This means it's a good chance you'll take damage while trying to damage the enemies. This game is alreadyNintendo Hard, but using Raphael as your main character takes this Up to Eleven and falls somewhere between Self-Imposed Challenge and outright Unwinnable.
The Turtles finally confront Shredder in the first film and he spends roughly three minutes defeating them with little difficulty. Then Splinter appears and defeats the Shredder in one move.
Super Shredder initially appears extremely menacing, and then he does himself in without the Turtles needing to do anything.
Badass Decay: The Shredder. He goes from defeating all the turtles in the first to getting beaten by an electric guitar in the sequel.
Continuity Lock-Out: The fourth movie introduces Karai and shows her leading the Foot now. However, unless you're familiar with the comics or the 2003 series, you will have no clue about her history with the Foot or Shredder. This is generally not a problem, but without the proper context, her anguished "You!" when she goes out of her to attack the Turtles upon their first encounter doesn't carry as much weight and may seem out of place.
Although it sort of works, since Leonardo is clearly as confused as to who she is and why she's so ticked off as the audience would be.
From the first movie, "Turtle Power" by Partners In Kryme. Although it incorrectly cites Raph as leader, it's still a rap of the highest caliber. It would be reused in the soundtrack CD of the third movie. Spunkadelic's "9.95," though to a much lesser extent, is also catchy in its own right, and would be reused in the trailer for the second movie.
The second—of course—features "The Ninja Rap" by Vanilla Ice, which asks you if you've "ever seen a turtle get down" and requests all ninjas to advance forward...in other words, "GO NINJA GO NINJA GO!"
TMNT features "Shell Shock" by Gym Class Heroes, which is catchier than it had any right to be.
Ensemble Darkhorse: Tokka and Rahzar. They were so popular, that they have since been added to future TMNT incarnations.
Franchise Original Sin: Teenage Mutant Ninja Turtles (2014) often gets flack for making April the focus of the story, though the film still centers around the turtles. The Turtles personalities are well done, but they don't get much character development. Lacking Casey Jonesnote who was MIA in Secret of the Ooze and putting in a villain (Eric Sacks) who had nothing to do with any of the comics or cartoons prior to that point was a mitigating factor too. The thing is that this problem can be found all the way back in the 1990 original. As pointed out by CinemaSins, Raphael is the only who gets a character arc of some sort, Leo gets some, and Donnie and Mikey don't get any at all. Plus, Danny, a minor character, had a sub-plot that while did not take over the whole film, was an odd decision. The reason why it wasn't noticeable back then was due to it being the Turtle's first film, the hype surrounding it, and a well written story with great practical effects and action scenes. The sequel, Secret of the Ooze, tried to fix the character development issue by putting the focus on Donnie's arcnote When the turtles find out they were created by accident., but it never really goes anywhere. Turtles III and TMNT (2007) both featured villains that had nothing to do with the comics or cartoons, albeit, the latter had Karai with hints of Shredder returning in a sequel that was never made. Tatsu wasn't in any prior media either, acting as a stand in for Karai, but he was the right hand man to Shredder, so that was okay. Karai was still obscure at the time unless one read the original comics, so that was understandable. Ooze had Tokka and Rahzar as expies for Bebop and Rocksteady, because Peter Laird and Kevin Eastman did not want them in the film. Teenage Mutant Ninja Turtles: Out of the Shadows, the sequel to the 2014 movie, is fixing that by dropping the Eric Sacks character entirely, adding in Bebop, Rocksteady, and Baxter Stockman. Villains that have appeared in the cartoons or comics. Also, the turtles themselves are going to be the main focus of the story and receive character development just like in other media..
Hilarious in Hindsight: Any sports fan over the last decade who's read the stories on steroid use can now look back on Raph's comment on Casey's Jose Canseco bat with a whole new meaning.
It was a two-for-one sale.
Donatello gets ragged on by his brothers for trying to make the word "Acapella" sound cool. Years later Eminem finishes what Don started, by using that word and the meaning behind it in a crucial moment against Papa Doc in 8 Mile .
In one fight scene, Casey defeats Tatsu by swinging a golf club at him, and he promptly kisses the club, saying, "I'll never call golf a dull game again." There's a ninja game for the Atari called Ninja Golf.
Nightmare Fuel: In the first movie The Shredder himself is made of Nightmare Fuel, he's like a faster and more agile version of Darth Vader with more pointy things.
Special Effect Failure: There was a slight decline between the suit quality between the first and second films (They still worked fine and looked rather impressive, but the executives made them dial back the details somewhat). In the first film each suit was individually made with a build and details unique to each turtle (Raphael has some tough-guy scars, Mikey is the shortest, Donatello is kind of chubby, and Leonardo is the slimmest turtle) In the second they had four (basically) identical suits with different heads for each turtle. The third film made the Turtles look like sock puppet frogs and Splinter like a poorly made Chuck E. Cheese.
Other failures that don't involve the animatronics (directly or indirectly) include:
In the first movie a clearly human hand swings in front of the camera as Donatello does a spin on his skateboard, there's a moment where you can clearly see a microphone cord dangling from Raphael's shell, and another where you can see the face of Donatello's actor peeking though his mouth.
In the third movie, the villain falls to his final demise into the water from off a cliff, and if you look closely you can clearly see that he doesn't hit the water, but that he disappears entirely with no splash to accompany the sound effect.
Tear Jerker: The campfire scene in the first movie is perhaps the film series' greatest tear jerker. It comes off as even more sad if you see it as how Splinter probably intended it to be: a final goodbye.
There's actually one at the beginning of the movie too where Splinter confronts Raphael about his anger and Raph breaks down in tears over his perceived failures.
They Wasted a Perfectly Good Plot: More like wasting a hinted plot in the fourth movie. The Sequel Hookhas Karai suggesting the Turtles will have to someday face the return of the Shredder, which fans probably would've preferred to being the actual plot instead of the one we got.
Visual Effects of Awesome: The animatronic suits and puppets from the first two movies, especially the first, still look unbelievably good even today; they should, since they were created by the Jim Henson creature shop and were the predecessors of all the current systems used for their full-bodied animatronics.
What an Idiot: The two footsoldiers that tried to drown Donatello in a fishtank. The look on his face while underwater screamed "How stupid are these guys."