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: The anime made Sakyo out to be a character you can almost sympathize with especially when he dies, while the manga makes him out to be a very rich businessman with very sick hobbies.
Anti-Climax Boss: After showing off his powers for a bit, Hagiri is suddenly defeated in one panel by Hiei's arrival. Gourmet, or rather Elder Toguro wearing his body is taken out in a similarly quick manner.
In the manga it's none other than Yomi. After a brief exchange in the fight, the story jumps to some later with Yusuke commenting on what happened.
Die for Our Ship: In spades. Keiko gets her fair share of this, but the biggest victim is actually Mukuro, who has beautifully written moments of warmth with Hiei (that differ in the manga and anime, but both have impact). Naturally, she is written off as a conceited whore that torments Hiei, allowing Kurama to come and rescue him.
Yoshihiro Togashi actually intended for Hiei and Mukuro to be a canon pairing, but the fan backlash that came about their Ship Tease was so severe that he canned it!
He also intended for Hiei and Kurama to be a canon pairing, but ditched it because similar relationships got too much backlash in his earlier works.
Let's not forget Maya Kitajima from the manga. Almost 90% of the few mentions she gets in the fandom are about how much of a "bitch" and a "slut" she is... merely for having a crush on her sempai Kurama!
Draco in Leather Pants: Sakyo gets this in canon in the anime, which gives him a romance with Shizuru and, as a result, an Alas, Poor Villain death. In the manga, he never gets involved with Shizuru at all, and certainly nobody mourns his passing.
Ending Fatigue: The final arc and epilogue somehow managed to drag on and feel rushed at the same time. The Three Kings arc ends right in the middle of Yusuke and Yomi's fight, with all the outcomes of the tournament simply told to the reader after the fact. And then after that is the multi-chapter epilogue that's basically just a large series of unnecessary one-shots (enough to take up an entire tankobon,) ending with one more conflict that's resolved easily, but once again ends right in the middle. Not to mention that Genkai's second and final death occurs off-panel during this part, and what would've been her very last appearance in the manga is after the cut-off point.
Oddly enough, the second judge during the Dark Tournament saga, Juri, proved to be a decently popular character despite only being in the show for the last quarter of that arc. The other judge, Koto, is also pretty well-liked.
Not to mention Chu and Jin, two characters who remain popular despite comparatively little screentime. Of course one of the factors of Chu's darkhorseness is because of his voice being Norio Wakamoto. And then this.note Ore no Chuu wa dorre da?. As well as being a Wild CardBadass turning the trope of the usual Training from Hellresults into a balanced and unpredictable fight.
And of course there's Hiei, who according to Word of God was just supposed to be a Starter Villain (clear with his more psychotic personality and "true demon form" showing), but whose popularity launched him to the status of one of the four main characters.
Foe Yay: Yusuke and every single main villain. Plus, Karasu spends the last parts of the Dark Tournament coming on to Kurama; "Human bodies are so frail... I know you fear what my touch could do to you... yet maybe you also want to know it." All this while stroking his hair from behind.
Ho Yay: Tons. Yu Yu is the granddaddy of shonen series using this trope to grab at the female demographic, and that's not even mentioning the canon gay couple. Not to mention Yusuke is neck-deep in Foe Yay at times. And let's not even start with Hiei and Kurama...
Jerk Ass Woobie: Hiei. It's not revealed until the third and final arc though.
Learning Hiei's backstory doesn't resurrect all the people he's killed, but it gives his actions meaning, and really turns him into a tragic hero.
Magnificent Bastard: Several of the villains, particularly Sakyou and Sensui, and Kurama, despite technically being a good guy, occasionally show aspects of this.
Moral Event Horizon: Even with his Freudian Excuse, some fans still can't forgive Toguro for his brutal murder of Genkai, massacring half the tournament stadium, and even his false-killing of Kuwabara.
Elder Toguro. Three words: Genkai puppet show.
Arguably taking over Makihara's body and torturing/killing him from the inside. And enjoying it thoroughly.
And then as Gourmet, he ate the mind reader, Murota, who had helped Yusuke and company out earlier.
What Ichigaki did to his "test subjects" will make you want to reach through the screen and strangle him. That, and his Annoying Laugh.
Narm: Even though YuYu Hakusho is usually good at avoiding this. It's really noticeable when it shows up. One such scene is with Sensui's sacred energy armor. Not only does it look funny but he just had to add to the narm by saying "I'm a living breathing sentient tank!"
Narm Charm: The Beautiful. Suzuka. Just watch Episode 50. Watching an old lady royally kick a gay clown's ass all over the place with nothing but her bare hands is pretty damn hilarious. Suzuka's antics along with Genkai's responses to them are really what makes it work.
Seasonal Rot: The Three Kings arc suffers from this. Common criticism involves Kuwabara being demoted to extra, the heroes not being heroic and an attempt to replicate the Dark Tournament arc but made most of the fights anti-climatic. The manga has it even worse at it showed about five battles that were very short.
Too Cool to Live: Raizen who was the strongest demon, even on his deathbed, he was still able to trounce the Big Bad in his descendant's body and then do the same to his same even minutes from death.
Younger Toguro and Karasu are villainous examples, is a demon with extreme brute strength and overwhelming presence and the latter is one of the few people that outsmarts Kurama as well as managing his overwhelming power with elegant grace.
The Untwist: In-universe. There is no one who is surprised by who the "mysterious masked fighter" is in the Dark Tournament saga.
Viewer Gender Confusion: Touya is a very pretty boy, which would be fine. But he's also an ice demon, and the best known race of ice demons has been established to be entirely female. He is established to be a different species but it's still enough that some fans swear he's female.
Come on guys, Touya gets a mention but Kurama doesn't? One of the DUB STUDIOS thought he was female!
The Woobie: Kiyoshi Mitarai, a.k.a. Seaman, suffered a great deal from bullying before joining Sensui. Also, Yukina in her introductory arc; she secretes jewels when she cries, and Tarukane will naturally go to great lengths to get them.
Woolseyism: "I know as much about games as I do hugs and puppies, and care for them even less. Wake me for the end of the world." The English dub is pure gold!
The implied romance between Younger Toguro and Genkai is much more accentuated in the dub, making their scenes far more heart-wrenching.
The supposed 100% strength of Toguro that was later surpassed by 100% over 100% was changed to "more like 85%" and TRUE 100% to make a bit more sense.
During the flashback of Itsuki meeting Sensui, Sensui asks if Itsuki has any regrets, and Itsuki names a TV show and a (at the time) celebrity who would be performing on it, which surprised Sensui because he watched the show too, and realized how... human Youkai were. They obviously couldn't name the TV show or celebrity in the dub because people wouldn't know who it is; but they still get the point across by having Itsuki say, "My favorite TV show will be airing its final episode tomorrow, and I want to see how it ends".
Both the English dub and the translation of the manga do an excellent job of translating Kurama's challenge to Kaito, in which if they say any of the forbidden letters—one is added from the back of the alphabet each minute.