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.
Alternate Character Interpretation: Is Tendou a God-Mode Sue played straight, with his boundless confidence and superhuman abilities (even without using the Masked Rider System)? A Parody Sue and partial deconstruction of the type (with his various failures, his strange obsessions, his inability to truly connect with others)? A Decoy Protagonist for Kagami (because Kagami is the one who actually espouses heroic values much better than him)?
Ending Fatigue: It's generally agreed that the plot haemorrhages coherence around episode 30.
Ensemble Darkhorse: Kagami spends most of the series being a complete Butt Monkey. But once he proves himself worthy of the Gatack Zecter, he becomes far more heroic in almost every way than Tendo, even as Tendo continues to be the series darling. The series does, however, lampshade that in some ways Kabuto and Gatack are equals and that Tendo respects Kagami, and perhaps only Kagami, because the Gatack Zecter is the only one the Hyper Sword doesn't steal, leaving it to belong only to Kagami.
Tsurugi Kamishiro is one of the more popular comic relief character in the series. His Large Ham tendencies and overall goofiness trying to "learn how the common man works" help. His storyline ending helps even more.
At times bordering on Parody Sue, especially in the series' more comical moments. The final episode has him walk to France to pick up some tofu on a lark.
Harsher in Hindsight: Tendou's remark at the rider anniversary segment at the end of one ep "If he's Stronger, than I'm strongest!" is no longer funny now that Araki Shigeru, Stronger's actor, has passed away.
Hell Is That Noise: The Worm's beetle-like clicking. At times it is tolerable, but it can reach extremely unbearable pitches.
The chef Worm Tendo fights has a really annoying noise that sounds like its'... farting.
Hilarious in Hindsight: Hidenori Tokuyama/Yaguruma will be the lead star in a movie based on the boxing manga Thanatos: Mushikera no Kobushi, which will also star Yūki Satō/Kagami possibly as the antagonist.
Yusuke Yamamoto/Kamishiro Tsurugi will play another eccentric "prince" AKA Tamaki Suoh in the Ouran High School Host Club live-action adaptation.
Ho Yay: Subtle with Tendou and Kagami, but more blatant in Yaguruma and Kageyama, especially after they become the Hopper Riders.
In a case of serious Paranoia Fuel, a Worm can become an almost perfect copy of anyone, including you. They are also stronger than you, can spit goo on you to kill you, and can slow down time to prevent you from escaping their clutches. The only way you can sense a worm is by their smell, which would be too late by then (unless you're a Kamen Rider, of course.)
Paranoia Fuel: The Worm. The fact that a race of over-6"-tall, hyper-advanced aliens with retractable tentacles for hands have successfully managed to infiltrate Japanese, and, by a larger extent, world society, perfectly imitate the humans they encounter right down to their memories, and kill those they replicate, can be severely unnerving.
Take that Up to Eleven with Tsurugi being the Scorpioworm without even realizing it. The only thing more unnerving than someone you know being a Worm is the possibility that you are a worm yourself and you don't even realize it.
Special Effect Failure: Gattack's battle damage in 44 is very obviously just extra bits stuck to the suit, with obvious edges.
There's various instances of transformations not melding very well (actor and suit actor standing in obviously different poses), sometimes bluescreen effects are sort of obvious, and some Worm are designed and fabricated better than others. Let's just say, some episodes obviously had higher budgets than others.
They Just Didn't Care: The designs for the various Kamen Rider suits display a sort of increasing amount of this. The Kabuto suit is possibly one of the best-looking Kamen Rider suits of the modern era, with Masked Form turning into Rider Form in a way that really displays the nature of how the Masked Rider System works. The amount of elaborate moving parts and clear effort on the part of the fabrication team declines from there, bottoming out at Sasword, whose Masked Form is just some halfhearted kibble velcroed to his Rider Form. It takes an upswing back up for Gatack, who's almost as good as Kabuto, but this is likely because that suit was designed and fabricated at the same time as Kabuto's. Theoretically there could be an in-universe explanation for this, but since it's never stated outright, it just looks like the design team got progressively more lazy.
Visual Effects of Awesome: The special effects are extremely impressive for a Tokusatsu series. From the cast-off and clock-up sequences to the choreography of the fight scenes, Kabuto, even after 5 years since it originally aired, is still considered to be one of the best-looking series in the Kamen Rider franchise.