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: Would it be a stretch to say that Miroku is more desperate than lecherous? After all, if he doesn't have an heir before the Wind Tunnel consumes him, well...
The old lady from the Demon's head arc, is she really a fraud or is it merely Obfuscating Stupidity and she is actually more powerful than she seems, especially since she's not unnerved by the demonic aura that keeps everyone in the main group on the edge,
Kikyou's theme is my personal favorite, an understated and haunting song that epitomizes traditional Japanese culture and aesthetics.
Designated Protagonist Syndrome: Kagome, as the average modern teenager via whom the audience mostly experiences the plot, can come across as much less interesting than the more exotic feudal-era characters she's surrounded by.
Sesshomaru. Character Development eventually renders him more sympathetic, but even prior to that he already had a substantial fanbase willing to overlook how in his early appearances he made several attempts at murdering Inuyasha and Kagome over a sword that he honestly didn't even need.
Naraku big time. Sesshomaru at least developed in time into a Good Is Not NiceAnti-Hero. Naraku has no such development, and whatever sympathetic traits he might have are overshadowed the fact he tortures, manipulates, and tries to kill every member of the main cast several times over.
Ear Worm: A good deal of the openings and endings.
Ending Fatigue: Many complain that around the third or fourth season the anime begins to drag, pace-wise. This is a notable complaint of many of Takahashi's work - namely that they're good, but tend to go nowhere fast. However, this doesn't happen as much in the manga, since the aforementioned seasons of the anime are filler-heavy.
Oddly, the second series has the reverse problem. Well over 100 chapters are condensed into a single season of 26 episodes.
Esoteric Happy Ending: To a degree, considering Inuyasha and Kagome. They're hinted to be married and are living content with one another, however the fact that Inuyasha will age much slower than Kagome is never mentioned, meaning that he'll most likely still be young looking when Kagome (and Sango and Miroku for that matter) becomes old people.
Evil Is Cool: Naraku after the Band of Seven arc, Goshinki in spite of being a Complete Monster, Ryukotsusei and the Band of Seven themselves.
Evil Is Sexy: Yura of The Hair was in TWO EPISODES, and she gained plenty of fanboys thanks to her sexy voice and Stripperific outfit. Kagura is also pretty attractive for a demoness and even gets Clothing Damage to the chest, twice!
Although the anime has her breasts covered up during her Clothing Damage, the manga has no problem showing her breasts completely uncovered! Cue nosebleeding fanboys.
Believe it or not, NARAKU himself has plenty of fangirls himself. Well when he isn't shown with Body Horror.
Kanna and Hakudoshi, desperate both having the appearance of ten year olds!
In fact, any normal looking evil demons are pretty sexy themselves.
Fanon: Sesshomaru is the Lord of the West, and he has a manor home or castle somewhere with servants and subjects. In the actual series he's a nomad with no home ever shown, he's not the ruler of any land anyway, though he is a daiyoukai (or at least becomes one by the end of the series), and his only servants are the ones you see with him all the time - and those mostly seem to have latched onto him in spite of his preference. (This seems to have originated with sketchy fan translations, but the notion remains entrenched in the fandom.)
In fact, even Sesshomaru's father never bore any such designation, either. He is only ever called "Inu no Taishou", and while this would literally translate as "Dog General", in spirit the title could be much more broadly interpreted, which the English version wisely represented with the more ambiguous "Great Dog Demon". He is never explicitly stated as having "ruled" the West, only to have resided there.
If fanfiction ever deals with Kagome growing older, she'll likely become some sort of doctor due to her experience patching up her friends. In Final Act she is seen learning herbalism from Kaede so she'll likely become the village healer.
Inuyasha's addiction to ramen. In the manga, he's seen eating it two times, and mentioning it tastes good. The anime shows his liking of it a little more but nothing remotely close to the “I’ll do anything for ramen” you see in fanfiction.
Inuyasha's tranformation to full youkai being triggered by anger. In canon it’s triggered by fear of dying not anger; the Unstoppable Rage comes afterwards.
In the absence of any Canon Names for them, it's common to see Inuyasha and Sesshoumaru's father referred to in the English-speaking fandom as "Inutaisho" (a corruption or mishearing of "Inu no Taisho" which is then used as a name instead of a title), and Sesshoumaru's mother is popularly called "Inu Kimi" (sometimes "Inu Kami"; the former, though more common, is probably a misspelling of the latter, which is Fangirl Japanese for "Dog God").
The sword Tessaiga is astonishingly phallic. It even throbs with warmth when "awakened" and grows hair on its hilt. Notable is that the sword is "awakened" by "protecting" a WOMAN. Not to mention powerful energies being "released" from it.
Growing the Beard: Once Kikyo is revived, a much more complex and intricate plot arose from what had previous been fully a Monster of the Week story. While it strongly contains the previous elements, the story would focus more on the group facing a far more intimate enemy than they had previously faced.
Hilarious in Hindsight: Sesshomaru is vaguely hinted to have developed feelings for Kagura (as she more canonly did for him), but she sadly dies before it can go anywhere. Some time later we're introduced to Sesshomaru's mother who, except having white hair, bears some distinct resemblance to Kagura in both looks and personality. Later it's been scientifically proven that we tend to fall for people reminding us of our parents...
Ho Yay: Contrasting with Jakotsu's Foe Yay to Inuyasha, his relationship with Bankotsu was much sweeter. Bankotsu himself held Jakotsu in high regards, and was PISSED when Renkotsu killed him.
Kagome is Type B: Because she is the easiest character for a girl to relate to, she is paired up with tons of characters while the author projects themselves onto her.
For his part, Sesshoumaru is Type A: He is the most lusted-after male character, so girls usually pair him with a female character that they can relate to (usually Kagome) and project themselves onto the female as a sort of Wish Fulfillment fantasy of putting themselves with him.
Les Yay: Episode 98. "Kikyo and Kagome: Alone in a Cave".
Like You Would Really Do It: To no one's surprise, our heroes were able to get the Sacred Jewel shard out of Kohaku's body without killing him.
Magnificent Bastard: Naraku, especially by the Band of Seven Arc, when he managed to get both Hakushin, a holy priest and the entire Band of Seven to serve him with a few good choices of words.
OSUWARI/SIT! In actuality, Kagome uses the control collar less and less over the series, not every time he says something off. It's also more played up in the anime than the manga, as she mostly stops using it the way she did earlier on around volume 7 or so.
Sango slapping Miroku for groping her. She actually stops slapping him after he proposes, which happens almost halfway through the story.
Moral Event Horizon: Naraku crosses it when he breaks up Inu Yasha and Kikyo, which leads the former to being pinned on a tree for 50 years and the latter to her death, and that's before he's even properly introduced.
Not really unintentionally funny so much as unintentionally cute; the dog demon forms of Sesshomaru and his and Inuyasha's father can come off as this rather than threatening due to the rather feminine-looking dog ears.
One-Scene Wonder: Due to the long nature of the series, several characters whose prominence is in one arc and never appear again are this, including an old exorcist woman from the Demon head arc, several possible Ship Tease interests and a great deal of demons and villains whose traits are as or more so interesting than the main villain and his overall scheme; most particularly the Band of Seven
Romantic Plot Tumor: The Kagome/Inuyasha/Kikyou love triangle takes up a lot of page and screen time, and is only resolved very late in an extremely long-running series, by which point many fans were heartily sick of it. This is not helped by the heaping amounts of Ship Tease making it fairly obvious which pairing would win in the end, it was just a matter of getting to that result.
Kagome and Kikyou both come in for quite a bit of hate from different ends of the fandom, most of it grounded in their mutually exclusive cases of Die for Our Ship.
Likewise Shipo, as a mouthy tagalong kid, and Koga, whose appearances inevitably touch of friction between Inuyasha and Kagome and whose introduction into the series leaves a shadow of Protagonist-Centered Morality over his subsequent characterization that makes him hard for some fans to accept.
Hojo, for his inability to catch a hint that Kagome isn't interested in him.
Ship-to-Ship Combat: The Kikyo/Inuyasha and Kagome/Inuyasha shippers hate each other, and if they were given the chance they would take up arms and start physically fighting. Then the shippers for any of those three with Koga, Sesshomaru, Rin and/or Kagura (or any of those four with one of the other three) would get pulled into it for one side or the other, and it would spiral out of a two-sided war into a multi-melee brawl. About the only shippers that wouldn't get involved are for Sango/Miroku, as the most official and least ambiguous of the series' pairings that isn't really threatening to or by any pairing...but there are periphery fandoms for pairings like Inuyasha/Sango and Miroku/Kagome. And let's not touch on the fandoms for Kagome with one of the Band of Seven, Koga or Inuyasha with Ayame, or any of the above with Naraku.
Some Anvils Need to Be Dropped: In-universe for Sesshoumaru: 1) Compassion is a good thing. 2) You don't need your brother's sword. 3) You are NOT infallible. 4) No, really. YOU DON'T NEED YOUR BROTHER'S SWORD.
They Wasted a Perfectly Good Plot: It's never explained why only Inuyasha can follow Kagome through time, which wastes some very interesting plots involving other characters and how they react to the present, especially with very dangerous characters like Naraku becoming a threat in the present rather than the Monster of the Week that occasionally shows up. Later justified as it is revealed in the first movie that the tree and the gateway that was made from it, were a sacred tree of time, so being bond to the tree, as well as being in close proximity to it is what allows Kagome and Inuyasha to travel through time. It's still a waste of a good idea though
Too Cool to Live: Inu no Taisho, BIG TIME, the third film shows how much more powerful and wiser than both of his sons, while being entirely Badass as he was at his death thralls to save Inuyasha's mother.
To elaborate, in his rescue attempt, he had used his two swords to mow down an army of soldiers and omniyoji with ease, revived Izayoi with the third, shot down with arrows and spent his last moments fighting a samurai in a collapsing buying castle. And this is after suffering fatal wounds from a powerful lightning spewing dragon demon of the highest caliber that he barely managed to seal away.
It's very easy to mistake Shippo for a girl at first, in both anime and manga.
Villain Sue: Naraku, thanks to the combination of his tendency to use puppets and lesser villains as pawns to accomplish his purposes and his talent for coming up with ways to escape beatdown after richly-deserved beatdown.
Wangst: Kagome. Sometimes very justifiable, sometimes... well, not. It should be noted that, despite that she complains a lot, if she goes overboard, she stops herself.
Another case could be made for Sesshomaru's dwelling of his dad not giving him the sword he wanted when most of the other characters have problems much worse.
What an Idiot: Hey Kikyo, if the bad guy is unable to kill you better don't reveal it to him or you'll probably be thrown from a cliff... No, don't give him the jewel's fragments, you are only making him stronger!
What Measure Is a Non-Badass?: Fans throwing a fit because Sango dared to get married and have kids, and calling Kagome "weak" because being physically weak somehow makes you a weak person overall, even though she was just a regular schoolgirl thrust in the feudal world and she STILL gets a lot stronger as time goes on.
Subverted in the actual series. Sango is a feminine, Yamato Nadeshiko family girl who is a demon slayer, and Kagura is a Lady of War that fights in a pretty kimono, her weapon is a pretty folding fan, and her attacks are all dances.