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: Kamen Rider Double
Anti-Climax Boss: Once Shotaro and Philip got their act together, Terror was surprisingly easy to beat in a straight fight, most likely due to the point of the Gaia Memory being to terrify your opponents into a state of helplessness.
Make that Double/Accel worked together. Once Ryu drew the Terror Dragon off and beat it, Ryubee's combat effectiveness was drastically reduced (also notice the fact that Ryubee can only create those liquids when Terror Dragon stayed in his headdress).
Utopia as well. Despite defeating Accel and the Taboo Dopant with no effort, Double makes surprisingly short work against him. Justified in that his strongest ability, absorbing emotions to power himself up, was used to overload him.
He gets defeated again in a spin-off movie, though this time it's because his opponent is Dead to Begin With and thus has no emotions to draw power from.
Awesome Music: Wailing Desperation, the then nameless One-Woman Wail from the prologue of the first episode; it was really short, but having been presented at a crucial and dramatic moment, it left quite an impact.
You can hear it again at the end of the first part of "The Girl...A", but with a more subdued and chilling arrangement as it accompanies an important Reveal.
Double's three Battle Themes, each with their own fitting style.
"Glorious Street", the Heaven's Tornado song from episodes 7 and 8.
Accel's Battle Theme, "Leave All Behind", based on his catchphrase.
"Nobody's Perfect", Kamen Rider Skull's theme; sung by the Chief himself, Koji Kikkawa, at the climax of "The B Carried on the Wind".
And following that, an upbeating sound of a music as Double starts fighting against the Beast Dopant in his new Super Mode.
That same music plays again in Accel Trial's debut.
"Extreme Dream" which wasn't used on the show until ten episodes after it was released.
"Extreme Dream" is a very good example of how to properly use this trope. It was only played twice over the course of the series, both times during particularly climatic battles, rather then being spammed every fight scene after Double get's his Super Mode.
Same can be applied to "Leave All Behind", which was also used a total of two times.
Base Breaker: The fandom's general opinion of Akiko earlier in the series. Very few people in the fandom took the middle ground, but both sides mellowed out over time.
Big Lipped Alligator Moment: Shotaro fools Jinno into running away from an imaginary yeti at the end of "J's Labyrinth". It turns out there really is one, and Shotaro and Akiko faint.
While this is more of an event in the Kamen Rider Decade movie ''All Riders vs. Dai-Shocker," no one should forget Double's debut himself where he plastered Shadow Moon himself when the game-breaking Decade and Rising Ultimate Kuuga cannot.
Broken Base: Arguably, the series ending. Some fans preferred the Bittersweet Ending of #48 to serve as the series ending, whereas other fans liked the real ending (#49) as it was.
Complete Monster: Isaka. He murdered various people, including Ryu's family, just to test his powers, modifies Gaia Memories to kill people so he can absorb their powers, has multiple connection ports all over his body (proving just how many people he's murdered for the aformentioned reason), and was the third-strongest Dopant after Terror and Utopia to exist during his lifetime. To add further proof of this, he was already corrupt enough for the Gaia Memory to not corrupt him further.
Jewel, even prior to becoming a Dopant. Not to the degree that Isaka was, but when you smash down windmills that little kids put up right in front of them, turn women into diamonds, and hold ransom someone the woman you love cares about you're still a horrible, horrible person.
Liar as well. His MO is breaking the dreams of people so he can collect their tears. he has no alternate motivation, he's just a literal sadist who loves causing misery. Dummy also qualifies. His plan was to kill people off and take on their personas to take their things. Yes, he's a coward, but he shows absolutely no remorse over it.
The Spider Dopant from Movie Wars Core. Holy christ, he basically reached the level of Isaka for this trope by spreading remote "bombs" around in Futo, making anyone they've devoted emotions to explode on touching them, so that no one will have a hand on his beloved Melisa anymore. From what was portrayed in the movie, he probably killed largest number of people on screen in Double's universe.
The Commander Dopant from W Returns: Accel. A Knight Templar who murders criminals, even if they've already surrendered. He coldly shoots an innocent person to lay the blame on Ryu, not caring whether or not the shot would be fatal. What truly pushes him into this role is kidnapping Akiko so he can murder her in front of him as the final part of his quest to drive Ryu to become a copy of him. Yes, he did lose his beloved wife to a criminal, but that does nothing to justify murdering people for pickpocketing and trying to murder someone's wife in front of him to turn him into the exact same person. He even outright admits that he's become evil, but doesn't care anymore. What's even more chilling is he's what Ryu could've been had Shotaro and Philip not been there.
Kamen Rider Eternal. He intended to turn an entire city into the living dead, then shot his mom dead when she tried to stop him. Sure, being forcibly resurrected would probably do some nasty stuff to your psyche, but that doesn't seem to excuse much the way he sees it. However, this is ultimately subverted when his realFreudian Excuse is revealed and that he was driven insane by the actions of....
Dr. Prospect/Eyes Dopant, who is on Isaka's level of sheer unspeakable evil, possibly WORSE! The man confined dozens of innocent people (kidnaping heavily implied) under threat of death, leaving them completely terrified of him. And he takes a sick satifaction in this! But he gets worse. He prepares to unleash his Heaven's Fall, a plan so horrific that even the aforementioned Utopia finds it brutal! It's letting loose a powerful electrical pulse, killing anyone in the entire village who isn't up to his standards for the project. When Katsumi stops that plan, Prospect reveals that was the least painful way he could think of to kill them. The eyes he implanted in them slaughtered the entire village when they escaped the village. Prospect then rubs salt in the wound at Katsumi's pain, laughing his head off about the fact he'd just murdered dozens of innocent people! These actions are so horrible, it drove Katsumi insane, making Prospect indirectly responsible for the events of The Movie.
Draco in Leather Pants: An In-Universe example. A whole V-Cinema is devoted to a girl from Kamen Rider Eternal's past popping out of nowhere and explaining to Shotaro and Phillip that Daido wasn't a bad guy and was just a Fallen Hero. Some people don't buy the tragic backstory.
It's mitigated by the fact that Shotaro and Philip still point out that Eternal did a lot of bad stuff and hurt Fuuto badly. Their memorial to him comes off as bittersweet, thinking about what could have been for a man who became a monster but could have been a hero, given different circumstances.
Specific examples from within the series include Kamen Rider Joker, Sokichi Narumi/Kamen Rider Skull, and Kirihiko.
Skull especially. His Figuarts is notorious for managing to find popularity with people who weren't fans of the franchise and fans who weren't collectors.
Epileptic Trees: No, for once, it's not the "Female Riders, No Survivors" one. A single picture of the Core Medals set off a wildfire, convincing people that Foundation X would be the next Shocker. Seriously. While it didn't get an expected pay off, one aspect of the foreshadowing, the "King Medal" does make it into the finale of OOO...
The much later appearance of Foundation X in Kamen Rider Fourze would eventually confirm that Double, OOO and Fourze all do in fact take place within the same canon.
Although Akiko did henshin into Double with no ill effects...unless you count getting her face being sucked by the Utopia Dopant as the ill effect.
She only henshined in a dream and it was to combat the Nightmare Dopant. Utopia Dopant came 17 episodes later and sucked the faces off of pretty much everyone in Fuuto.
Fan Dumb: There's a lot of hate going around for Accel Trial, calling him a rip-off of Faiz Accel just because both have speed-based powers and have similar names. Never mind that they're all Kamen Riders anyway, or that it's obviously not uncommon for more than one rider to have similar powers, and that there are significant differences between the two.
Oddly, you don't hear this about Kabuto. He's another red, silver, and black protagonist Rider with armor in the exact same places, headlight eyes, and a speed-up power that's basically taking Faiz's gimmick further.
Hilarious in Hindsight: While no crossover with Samurai Sentai Shinkenger has been planned (unlike Kamen Rider Decade prior), two unintended parallels have surfaced - Memory Gadgets attach to Double's weapons while each carry one of the season's collectible items (the Gaia Memories much like the Shinkenmaru and Inroumaru with their Hiden Discs), and both Kirihiko and Mako's father married into their respective families.
Three now. In Shinkenger, it turned out that the real head of the Shiba family is a girl - fan reaction is mostly positive, but you let Akiko take charge of ONE detective agency, and out come the pitchforks...
In Kamen Rider Blade, Hirose attempts to crack the BOARD database and eventually figures out the password: "Double Joker".
Blade's Big Bad is, in fact, the Joker Undead. Not to mention that as Kamen Rider Chalice, he uses wind powers. Guess what Double's main form is called.
Ho Yay: Shotaro Hidari & Philip. The fact they share a body when in Extreme (or when just being Kamen Rider W) might have helped, but these two have generated a fair amount of theories based on their behavior.
Jerkass Woobie: Did bad stuff happen to the Puppeteer Dopant? Yes. Should you feel pity for the poor guy? Yes. Does that excuse any of the shit he pulls? No.
Mood Whiplash: Made the previous reigning king of this in the franchise, Kamen Rider Kabuto, look like an amateur effort. One example is how there would be serious scenes of Shotaro brooding over his mentor's death sandwiched between scenes of Akiko running around acting like a Looney Tunes character high on crystal meth.
Moral Event Horizon: If the powers of the Utopia Dopant don't convince you that Jun is a complete monster, then the fact that he went after Shotaro and Philip's friends and sucked their faces off will convince you to want to see Jun get his ass handed to.
Commander kidnapping Akiko with the intention to kill her in front of Terui to make Terui the copy of him. The fact she's an innocent person who has done nothing wrong is what makes him go from a simple Knight Templar to a Complete Monster.
Narm: In The B Carried On The Wind, when Shotaro and Philip were walking towards the Beast Dopant near the end, Philip falls down, as usual when they transformed. What makes it hilarious is that they tranform in a semi-slowmo fashion, with the music "Nobody's Perfect", sung by Koji Kikkawa, the actor who plays Sokichi Narumi, their boss, and Philip literally falls on his face...In slowmo.
Even before that part, we got Terui being handed his behind on a platter. Slo-mo along the song. Pure gold.
Nausea Fuel: Deliberately invoked with "Find the C"'s Cockroach Dopant, whose apparently decorative appendages sometimes flutter involuntarily like actual cockroaches.
Nightmare Fuel: The Terror Dopant has the ability to make reality bleed the stuff.
Special Effect Failure: Isaka's defeat. You'd think that by now they've stopped getting sloppy with the enemies exploding.
The movie has an example with all of Katsumi Daido's transformations. It's painfully obvious that he magically grows a foot whenever he becomes Eternal.
This Is Your Premise on Drugs: The Delusion Diaries, little shorts of Shotaro having really bizarre daydreams. Entries include 'what if Akiko was a little sister' (featuring the cast as his family, complete with Ryu as a housewife and the Weather Dopant as his father), 'what if Akiko was an idol' (ending in Akiko marrying the Triceratops Dopant) and 'what will the agency be like in the future' (featuring old man Shotaro, old woman Akiko, Ryu as a ghost haunting the agency, and Philip having not aged a day due to being data.)
Values Dissonance: Some western fans deride Kirihiko as a Henpecked Husband because he is deferential to Saeko, took her name after their marriage and has been physically abused by her on at least one occasion, along with the implication that it wasn't the first time. A Japanese audience would be less inclined to see him as weak, since their society emphasises reverence towards social superiors and loyalty to one's employer.
Hell, you don't have to be an expert on Japanese culture to see it working this way. Saeko is the Big Bad's daughter, and Kirihiko is just a good Memory salesman. If Darth Vader had a daughter he actually liked and doted on and a pretty decent officer (sorta guy Vader won't hesitate to strangle) married her, if the officer thought he'd be her equal, he's Too Dumb to Live. If you're brave enough, it's still quite a desirable position - fifth-highest member of the organization. And if he hadn't acted respectful, there is no way he would have had a chance of getting that high in the first place.
What Do You Mean, It's Not Symbolic?: Accel's jacket carries the slogan "Spiritual state of nothingness makes even itself fire cool", which is paraphrased from a Buddhist philosophy.
The Woobie: Akiko, especially after she finds out why her father could never see her again in Core.