Overlapping with Depending on the Writer, thanks to the numerous and conflicting (even back in 1984) continuities and depictions of Generation 1 characters, it's rare that you'll find more than two portrayals of the same character that match up perfectly, so how certain characters act all depends on your continuity of choice.
Is Shockwave loyal to Megatron as he is in the cartoon, or a logic-obsessed Starscream that's more effective than Starscream himself as in the comics and his original toy bio?
Ratbat. He's a voiceless servant to Soundwave in the original cartoon, but he becomes Decepticon leader for a time in the original comics. Later continuities have tried to meld both interpretations for one backstory, where Ratbat is usually of high power before becoming a servant of Soundwave.
Starscream: does he want Megatron's postition, or Megatron's respect? The in-universe explanation (at least some of the time) is that, while Starscream is a traitorous schemer, Megatron keeps him because he reminds Megatron of the need to watch his own back and keep his power protected at all costs.
Is Grimlock really stupid? Or does he just pretend to be stupid to throw his enemies off guard? Another interpretation is that Grimlock is quite intelligent but is unable to speak properly due to a malfunction in his speech processor, giving him a variant of Broca's aphasia.
Soundwave is popularly seen as Megatron's loyal Yes-Man, but his toy bio paints him as an unscrupulous blackmailer who prides on digging up dirt on people and using it against them. Then there's his speech - sometimes his speech is written like his cartoon Machine Monotone talk, while other times his speech patterns seem no different to other characters.
Audience Shift: Most current material based on Generation 1, specifically comics, toys, and re-releases of the animated series, is aimed towards fans who grew up with the franchise rather than the children that it was originally intended for.
Awesome Ego: Megatron/Galvatron and Starscream, all the way. Also Grimlock when his intelligence gets temporarily boosted.
Justified, it you think about it, as Devastator is frequently portrayed as the first Combiner and a prototype.
Of Course, then you look at Menasor. Menasor was one of the most powerful combiners, taking down his counterpart Superion in their debut, and only losing when facing both Superion and Omega Supreme, his next appearance had him take down Bruticus, come Season 3, a few shots to the back took him down.
Scourge and the Sweeps in Season 3. In the Movie, they tore apartUltra Magnus, in the series, they're Galvatron's punching bag.
Optimus in "The Rebirth", where he comes off as a bit of weary old man and never really engages in battle like he did before. The bad part about this is that it could've easily been worked into a character arc, with him being shaken by dying and coming back. Except the season 3 finale beforehand had Prime get over it and save the day all but singlehanded in one of the show's biggest Awesome Moments, so there was no longer any excuse.
Megatron - viewed by some as a menacing, Badass villain, and criticized by others for being a General Failure (at least in the series pre-Movie).
Arcee is either praised for being the first notable female Autobot in the franchise who is a regularly appearing character or is loathed for the feminine cliches she's often subjected to.
Bizarro Episode: Quite a bunch, most notably Carnage in C Minor (where the Decepticons try to collect the three notes of a harmony that can destroy the Autobots from a race of aliens that always sing when they speak) and the notorious B.O.T. (a pair of extremely rude high school boys and a nerdy girl they are partnered with create a crude robot for their science project and inadvertently give it the brain of the Combaticon Brawl).
Broken Base: While G1 is the most iconic incarnation of Transformers apart from the live-action film series, the Transformers fanbase is up in arms over whether it was a legitimately good cartoon, a deliciously cornyGuilty Pleasure, or a poorly-made toy commercial that is blindly supported due to nostalgia. Debates of this type also include how it compares to other Transformers series.
Unicron is an ancient planet-eating Transformer that was created by a Mad Scientist called Primacron. Primacron created Unicron to help him take over the universe, but he rebelled and destroyed Primacron's lab. Unicron travelled through space and devoured many inhabited worlds, including the planet of Lithone. After learning of Optimus Prime's death and his passing of the Matrix of Leadership, Unicron tracked down Megatron and tasked him to destroy it, as it was the only thing that could stand in his way. Torturing Megatron into accepting his deal, Unicron reformatted him into Galvatron and made him more susceptible to his psychic assaults. Galvatron, tired of being Unicron's pawn, tried to use the Matrix to turn Unicron into his slave, but it had no effect in his hands. In retaliation, Unicron started destroying Cybertron and attacked both Autobot and Decepticon alike. Unicron was eventually defeated by a Matrix-wielding Rodimus and only his head remained to orbit Cybertron, a testament to the Transformer that made even the mighty Megatron beg for mercy.
Ensemble Darkhorse: Sideswipe is insanely popular, despite his fairly generic bio and being Out of Focus for the entire series. Most people credit this with him having a pretty great toy for the time. Skywarp is in much the same boat.
Fan Nickname - Starscream = Screamer, Optimus Prime = Robo Jesus, Megatron = Megs
Although Skywarp did call him "Screamer" in one episode.
And Megatron has been referred to as "Megs" on occasion. We're still waiting for someone to call Optimus "Robo Jesus".
Ramjet, Thrust and Dirge were nicknamed "the Coneheads" because of their cone shaped-heads, at least in the cartoons; their boxart and instructions in the toyline depict their heads as normal-looking Seekers.
First Installment Wins: Until the live-action movies came along and caused Adaptation Displacement, Generation 1 was synonymous with the Transformers brand itself; even to this day, it's the most well-known incarnation apart from the movies, and there are many fans who attest that it remains the most iconic and definitive.
Foe Yay: Megatron never did punish Starscream that much for his disloyalty, usually just a verbal lashing or the occassional physical altercation... until he became Galvatron, that is.
Fridge Brilliance: During "The Key to Vector Sigma" the military thinks the Stunticons are the Autobots. Sounds stupid with Decepticons like the Constructicons and the Triple Changers, until you realize that up until this episode the Decepticons had no normal ground vehicles as transformers. As this was cars and a big rig, which means it practically has the Autobots written all over it.
"Funny Aneurysm" Moment: At the end of "Only Human", which takes place in the then-future year 2006, "Old Snake"* who is all but stated to be a future version of Cobra Commander laments that "they simply don't make terrorists like they used to..." as the episode's villains are taken away. Even beyond 2006, real life has proven that they do make terrorists like they used to.
Growing the Beard: Subverted. Season 2 showed a lot of signs of improvement (stronger and bigger scale plots, more backstory, more spotlight episodes and characterization, better animation, etc.) but the last few episodes of the season and season 3 promptly took a nosedive in quality, bar a few really stand-out episodes. Note however that there are some who feel season three has merit; see Seasonal Rot below for more.
Hell Is That Noise: In "Five Faces of Darkness, Part 1," Cyclonus and Scourge intend to bring back Galvatron and they begin their search at his last known location: Unicron's floating head.
Cyclonus: There's nothing to fear. Unicron is dead. (They hear a groan) Cyclonus: Must be the wind. Scourge: There is no wind in space. Cyclonus: Quiet!
In "Hoist Goes Hollywood," Hoist and several other Autobots get to be in an action movie. Unfortunately for them, the human characters initially take precedence over their bit parts, the director seems to have little respect for the Autobots (at least early on) and there's a good deal of pyrotechnics in the movie. Sounds familiar.
The references to Brawn being a Robot Chicken in "Fire on the Mountain". Quite a few Robot Chicken sketches involved Transformers characters.
In "B.O.T." there's a junkyard operator who really looks a lot like Luigi.
In "Only Human", human Arcee borrowed a motorcycle. Later iterations of Arcee, such as in Transformers Prime, transform into motorcycles themselves.
The episode "Autobot Spike" is pretty hilarious to watch after seeing the movie and the third season for two reasons. One is that the doctor seen tending to the injured Spike Witwicky bears a striking resemblance to Spike's adult self. The other reason is because the episode ends with Bumblebee asking what would happen if an Autobot's mind was put into a human body, with the aforementioned "Only Human" having some of the Autobots becoming human.
In "The Girl Who Loved Powerglide", Powerglide at one point says "It's hero time".
Rodimus Prime admits to dreaming about Optimus. His own voice actor (jokingly) claimed the character was gay, despite many incarnations of the character being romantically-linked to Arcee.
There's also Megatron and Soundwave. Soundwave is slavishly loyal to Megatron and is the sole person that Megatron never abuses or insults (in fact he heaps praise on the guy). This extends to after Megatron became Galvatron, including a scene where the two hold hands as they fly. It's common for fans to joke that the two are secretly lovers.
And then there's Megatron and Starscream, who fight and bicker like an old married couple, with Starscream as the whining nagging wife to Megatron's ever agitated husband. Taking the aforementioned subtext between Megatron and Soundwave into account one has to wonder if Megatron effectively dumped Starscream for Soundwave and Starscream simply never got over it. At one point Starscream actually asked Megatron "Aren't you happy to see me?"
Jerkass Woobie: The Constructicons, who are only evil because Megatron reprogrammed them against their will.
"Soundwave superior. Constructicons inferior." Which in turn led to "Soundwave superior, [insert name] inferior."
Also from the Evil Twin episode: Which Prime is the real Prime? LET'S HAVE A RACE.
GEEWUN, a fan term describing those who overglorify G1 (usually due to nostalgia) and bash most other Transformers incarnations, most infamously the Transformers Film Series. Notably, this term cross-pollinated into the Pokémon fandom as "Genwun", and is used to describe fans who are similarly attached to the earliest incarnations of the franchise to the exclusion of others.
On the inverse is REEDUN, for fans who insist everything be constantly changed and whine incessantly when any new toy, fiction or anything else calls back too heavily to the original series. Yes, they can be almost as bad.
Megatron famously crossed it in the movie when he killed Optimus, though one could he say he crossed it far earlier with the Robo-Smasher (aka. the device he used to horrifically brainwash the peaceful Constructicons into Decepticons and destroy Crystal City). For Blitzwing at least, the deal with the Quintessons was the point of no return for Galvatron.
Nightmare Retardant: Megatron, you know that scope that turns into his iconic black hole gun? That scope and other accessories aren't from a real Walther P38 but were made up by the prop department of The Man from U.N.C.L.E., which means the most fearsome Decepticon of them all either turns into a TV prop, or more likely some kid's toy based on a TV prop.note This is actually made explicit in the original Japanese Microchange toy he's based on, where they're all tiny aliens who disguise themselves as toys and other household objects in a little boy's bedroom. Soundwave, Rumble/Frenzy, Laserbeak/Buzzsaw, Ravage, Blaster, and Perceptor also came from this line, as did an unproduced Planet-Robo that eventually became Unicron. Incidentally this is also why the original Bumblebee and the other 1984 Mini-Cars (IE Cliffjumper, Brawn) had such goofy, Penny Racer-style proportions, since they were meant to represent toy cars.
One-Scene Wonder: Hauler's appearance in cartoon was very brief. However, his similarity to both Grapple and the Constructicons led to various theories about his origins, before the character got an official background story which depicts him as a rogue member of the Constructicons, complete with an E-HOBBY exclusive redeco of Grapple.
Offscreen Moment of Awesome: In the cartoon episode The Key To Vector Sigma, Shockwave apparently defeated Omega Supreme in battle (offscreen).
Rodimus Prime is hated for replacing Optimus Prime while failing to replicate the traits that made him such a popular character. He never developed his own leadership style and lost the more interesting Hot-Blooded personality that he had as Hot Rod. It really doesn't help that, in-story, he was never even supposed to be leader; Optimus explicitly named Ultra Magnus as his successor, not Hot Rod. Then you have episodes like "Fight or Flee", in which he displays a big example of Moral Dissonance by blowing up Sandstorm's peaceful planet just to stop the Decepticons getting it, then saying he prefers Cybertron for not being so "perfect" to Sandstorm's face as he's grieving. And this is at the episode's end, so he never gets called out on this. Fans almost universally consider his best decision as leader to be reviving Optimus and than stepping down from his position. Yeah. Other versions of the character aren't this hated, but they either don't replace Optimus or keep the "Hot Rod" personality and just change their name.
Daniel and Wheelie are hated for replacing Spike and Bumblebee as the Kid-Appeal Characters, but falling into the exact pitfalls that Spike and 'Bee avoided, like being too young and having annoying voices.
Galvatron generally gets the least of this (possibly because he technically is Megatron, just in a different form), but many still prefer Megatron due to feeling that Galvatron came off as less competent and didn't have as many interesting dynamics with his troops.
Rooting for the Empire: While the Autobots are hardly unpopular (especially Optimus Prime as demonstrated below), the Decepticons sell as many toys and are often considered more developed and less gimmicky or bland characters than some of the heroes. Megatron, Soundwave, Starscream, Galvatron, and Cyclonus especially. That the Autobots and some of their allies were prone to odd moments of Moral Dissonance exacerbated this a little.
Saved by the Fans: Optimus Prime is probably the most famous example of this, being brought back after the massive backlash from being Killed Off for Real in the movie. Though in this case it was less "Saved by the fans" and more "Saved by letters of complaint from the angry moms of traumatized children". They did this in spite of the cartoon being Merchandise-Driven, as when Optimus was resurrected, he had no toy on the shelves (bar any unsold Optimus Prime toys, or the fact that the toy was actually in production due to its popularity, but not publicly advertised beyond voice-overs in commercials providing narration for the new Autobot toys). Optimus would not get another toy until the 1988 Powermaster toy.
Rolan and Martin from the infamous episode "B.O.T." are generally disliked for being far more obnoxious and mean-spirited than the Autobots' other human allies. They are even nicknamed "future serial killers" on the Transformers Wiki.
Seasonal Rot: Season 3 is widely considered a step down from the previous two seasons due to killing off/writing out most of the old cast in favor of new toys, drastically changing the setting and style, and the animation becoming worse than ever (which can be laid at the feet of South Korean studio AKOM, which often produced subpar artwork and numerous coloring, model, and continuity errors, though with a slightly higher frame rate than Toei-animated episodes). However there are a few episodes that are given seen as really good and some parts of the fandom feel that Season 3 actually made some improvements over Season 2, like having a more manageable cast size or bigger scale plots. In addition, Toei churned out episodes with VERY beautiful art, and the episode "Call of the Primatives" remains the best-animated episode of the series; too bad the studio who animated it is still unidentified to this day.
In particular, the episode "Carnage in C-Minor". Sure, it has no end of animation, technical and continuity errors, but it has a good plot (as well as a little Fridge Horror at the end) and the errors have nothing to do with the plot itself.
"A Prime Problem" is another example because the plot is completely ludicrous (everyone has the Idiot Ball) and Optimus Prime hilariously flubs Spike and Trailbreaker's names (Spike as "Splick", and Trailbreaker as "Trailblazer"; the latter case is Hilarious in Hindsight, though, as the name "Trailblazer" was used interchangeably with "Trailcutter" when Hasbro lost the trademark to the name "Trailbreaker". At least neither are as bad as "B.O.T.".
Given one Prime is actually controlled by Megatron and none of the other Autobots can tell which of the two "is real" until The Reveal (Megatron's "Prime" angrily remarks about a captive Spike, "HE'S UNIMPORTANT!" which get the Autobots to see he's "phony"—the "Real Prime" would have dropped everything for Spike), it's understandable.
"B.O.T" probably qualifies as well, if not for just plain bad, due to the massive Idiot Plot around three of the dumbest humans to ever exist and their stupidity seemingly affecting the rest of the cast as the episode goes on. Two of the humans, Roland and Martin, are the most unrepentant Jerkasses in the series, dragging the third human (Elise) around (at the end of the episode, they tape her mouth shut and drag her away while the Autobots do NOTHING) and using a laser that can kill people as a prank. A prime candidate for Snark Bait.
Special Effects Failure: More often than not combined with Off Model. Much of this was caused by the low-budget Korean studio AKOM in three second season episodes, much of season three, and all three fourth season episodes.
Squick: Kiss Players, which contains not only lolicon, but penis tongues.
Starscream being resurrected by Unicron and then being blasted into space is the last we see of him. One favorite fanfiction topic has Starscream returning and creating trouble for Galvatron, or creating his own Decepticon splinter faction.
Season Four seemed like it was setting upon a return to the classic formula, with Optimus Prime returned for good and Galvatron rerailed closer to his more lucid and cunning Megatron self. Unfortunately all but a three part special came of it. Headmasters at least played with it a little longer.
Villain Decay: Particularly prevalent with combiner teams, but also with characters representing other gimmicks, such as Triple-Changers. Devastator was unstoppable in early episodes, and in more than one episode unbeatable even by the entire Autobot team. Later, he could be broken up by a single shot from Perceptor. This effect was largely symmetrical, as Autobot combiners were also brought in to replace the formerly formidable older ones. Multiple Autobot characters have been referred to as their "last line of defence", including Omega Supreme and Metroplex.
What an Idiot: Multiple examples from both the Autobots and the Decepticons and even the humans who get caught in the crossfire.