Despite how easy it is to criticize, critics (think Roger Ebert) have a hard job of it. They need to be as fair as possible in their assessments not just to gain and maintain credibility in their audience's eyes, but also because it can completely overshadow and ruin the review itself as a work.
Granted, critics are (probably) human and have pet peeves or favorites, and good/bad performances and dialogue are certainly open to criticism, but when these feelings get out of hand and leak into the review, things get worse.
If the critic has a strong bias against or in favor of a genre, style, director, actor, or what have you, and they allow that acerbic vitriol or blind admiration to fill their review, they're driving a Bias Steamroller. The review often stops being about the work and becomes about the element that inspires the bias; essentially boiling down to "I love (or hate) A; since work B has A in it, I love (or hate) work B; therefore you should (not) watch it."
This may be because they hate a particular trope or just likes hating in general. Then again, they may be a fan of the series/franchise/creator who, out of loyalty, never fails to give the most glowing of praise. In any case, the damage to the review is such that it becomes too biased to be useful. (When a reviewer does this, people tend to ignore it, when fans often use it, it becomes a justified use of Don't Like, Don't Read.)
In some of the worst cases, the reviewer may fixate on a particular thing they liked or disliked and give the impression that they might actually not have seen the work in question. And there are times where they actually haven't seen much of it. More honest reviewers will at least admit to their biases up front and acknowledge that any review is going to be slanted - if a reviewer says they think boxing is the most boring sport in the world, Sylvester Stallone is the worst actor in history and Philadelphia should be erased from the map the reader will realise they arent going to be able to give Rocky a fair shake and proceed on that basis when reading or watching the review.
Part of the reason this trope exists, is that a review that accurately informs the readers about a subject's objective qualities, and allows them to make an informed purchasing decision, can be very boring. A hugely biased review, by contrast, may not be useful qua review, but may be entertaining enough to keep the readers coming back.
Note that this happens a lot outside of media criticism. Because it's just easier to remember particularly noticeable or dramatic experiences and events, this routinely happens in both positive and negative ways to people like politicians and celebrities.
Compare/Contrast Unpleasable Fanbase.
Peruse the Ghetto Index to see examples of when many critics develop a bias against entire genres.
Examples (sorted by medium being reviewed):
- Atop the Fourth Wall host Linkara is decidedly not a fan of anti-heroes in comics. He primarily views superhero comics as escapism (not that he has a problem with them tackling serious subjects or challenging the viewpoint of the reader) and really thinks that anyone deserving of the title "superhero" should at least be trying to take the moral high road in any given situation. This can sometimes cause him to be overly harsh to Marvel comics vs. DC comics because DC doesn't have nearly as many anti-heroes, whereas Marvel has several and even has previous boy scouts like Cyclops become this. This bias also colors any review of any Darker and Edgier comic. He also really hates it when superheroes are killed off, but understands why it happens in some cases.
- Movieguide.com identifies its Bias Steamroller right up front, not trying to pretend it doesn't have one. It reviews films from a fundamentalist Christian perspective; for instance, they criticize The Golden Compass for its "strong pagan themes".
- Roger Ebert:
- He considered movies where young children are apparently unfazed about committing serious acts of violence to be "morally reprehensible." This was a major reason why he was not a fan of the Home Alone series, why he only gave Kick-Ass a one-star review (in contrast to most critics), and why he tore apart The Powerpuff Girls Movie.
- Ebert has expressed regret for his previous bias against the Spaghetti Western genre, particularly for how it drove him to give The Good, the Bad and the Ugly a 3-star score despite writing what he acknowledged was a 4-star review.
- Ebert's disdain over video games led to a noticeable bias against movies based on or inspired by Video Games. When asked about not reviewing Scott Pilgrim vs. The World, Ebert admitted to the bias (and a writing sabbatical). He added that he was still able to sleep despite not reviewing the movie.
- While guest hosting on Siskel and Ebert, Ain't It Cool News founder Harry Knowles panned SLC Punk! because he disliked the star, Matthew Lillard. Ebert, who praised the film, made this trope rather blunt when summarizing their takes at the end of the episode. Knowles was not invited back for another episode.
- Troy Patterson of Slate made no attempt to hide his disdain for the fantasy genre while reviewing Game of Thrones, resulting in Patterson getting comments (before they were disabled and removed) ranging from angry fans bashing Patterson for "not getting it" to others expressing confusion as to why Patterson was reviewing the series when he clearly wasn't going to make any effort at being objective or give it a chance. Patterson was reportedly so rattled by the experience that he recused himself from reviewing the series any further.
- Yahtzee of Zero Punctuation doesn't care for anime or anime-themed games, and tends to be pretty harsh on them. He openly admits this and tends to avoid reviewing them in the first place, but some games aren't as obvious and get through. When they do, he tends to focus on the anime elements, and overlooks some obvious answers or flaws in his arguments. (For example, when reviewing Valkyria Chronicles, he jumped to the conclusion that all the characters were teenagers, when the game makes it clear that they are in their early-to-mid 20s, and one of them has just come back from college.)
- He also has an expressed disdain for Turn-Based Combat, particularly in JRPG's, and will usually take some time out of any relevant review to complain about how stupid, boring and unrealistic it is.
- However, he seems to be undergoing some change about both counts, with his 'Best/Worst/Blandest of 2017' video including Persona 5 - a heavily-animesque game with a turn-based combat-system - in the Best-list... much to his own surprise. (Though, admittedly, still only in 5th place, and he said that he liked all the parts that "distracted" from it being a JRPG, such as likeable characters that you get invested in.)
- Video Game Dunkey is quite outspoken about not liking JRPG's due to the anime influences it has, and thus tends to be critical of the genre when he does discuss them. This came to a head with his Octopath Traveler review, where he spent most of the video complaining about the genre, with only small parts of his video discussing the game itself. The community itself was not too thrilled at the video.
- JoCat makes no secret of his love of the Sword and Shield in his Crap Guides to Monster Hunter: World and Dungeons & Dragons, to the point of insulting and putting down other weapons/classes just as much as he advises on their proper use.
- MarioTehPlumber is a Troll, so naturally his "reviews" of Sonic the Hedgehog and Nintendo games on YouTube are absolutely full of bias. Most infamously, his extreme hatred of anything that he perceives to be even remotely sexual, even if it's not supposed to be (e.g. referring to Sonic's longer quills in his modern design from Sonic Adventure onwards as "Hentai quills" and accusing anybody who enjoys any Sonic game with the current design of "liking to shove his quills up their asses"). This bias takes priority over the gameplay itself in the "reviews", owing to MarioTehPlumber's "Character design > Gameplay" beliefs.
- Parodied by The Onion's video review series with Peter Rosenthal, who plays a character for each review whose personal biases and experiences, some of which are very odd, are often allowed to completely dominate his opinion of a movie. For his review of Home Alone he's a gun fanatic who spends much of the review complaining about Kevin not shooting the burglars, he spends the The Hobbit: The Desolation of Smaug review comparing it unfavorably to a series of fantasy books he himself wrote, and gives a good review to Antichrist for its relatable depiction of the normal human stages of grief.
As I watched this film I found myself growing ever more incensed at the Ghostbusters for delaying God's retribution by storing ghosts in their Ecto-containment unit instead of sending the souls back to Perdition to suffer with all the other idolaters, fortune-tellers, and sodomites.
- The Mysterious Mr. Enter is another reviewer known for admitting he has a Bias Steamroller. Notoriously, one of the qualifications for a show being an "Animated Atrocity" is for it using Toilet Humor in excessive amounts (Mega Babies, a So Okay, It's Average series that used excessive toilet humor, became the cartoon community's punching bag for a bit as a result of this), something considered "meh" by professional critics' standards.
- Nostalgia Critic-like fanfiction critic The Fic Critic (no, not The Fanfic Critic nor The FanFiction Critic) has noted that he tends to be biased against fics that act meanly towards certain characters or treats them badly, especially ones he likes. One noteworthy example was when he went from disdainful but amused at the stupidity of Web Of Shadows, a Spider-Man/X-Men Evolution crossover Mary Sue Parody fic, to outright anger and chain swearing after Carlie Cooper called Mary Jane Watson, who he admitted is one of his favorite Spider-Man supporting characters, a slutty model who dresses like a street walker. His reaction to her calling Mary Jane this is one of the few times he went from snarky to outright pissed, and ended up giving that chapter a "Fuck/10".
- Feminist Frequency has a strong bias against violent media in all forms, and argued True Grit and Mad Max: Fury Road were anti-feminist because of their violence.