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.
Danyl Johnson did fairly well in the 2009 series, coming fourth overall, but it's fair to say that he never quite lived up to the promise of his initial audition.
Janet Devlin was considered to be the runaway favourite during the early stages of the 2011 series. However, her performances started to get worse as the series went on, eventually resulting in her falling apart spectacularly in the third-last week, and being voted off the show.
Chico Slimani from Series 2 was the show's first major example of this, being obviously less vocally talented than pretty much every other finalist, yet constantly being saved from elimination, eventually culminating in Simon Cowell eliminating his own act (The Conway Sisters) in favour of Chico, who was in Sharon Osbourne's category.
The Conway Sisters were not exactly popular with the public either. They had been in the bottom two in both the previous two weeks, with the judges keeping them in over hot favourite Maria Lawson in the first showdown, and the popular Nicholas Dorsett in the second. The fact that they had worked with Louis Walsh's group Westlife increased the viewers anger.
2011 provided Misha B. This isn't to say that she was a bad singer, but her mentor Kelly Rowland clearly favored her over her other acts. It got worse after she lost public support following accusations of bullying and wound up in the bottom two on multiple occaisions, but remained in the competition until the final few weeks; when the judges acknowledged that even if Misha got to the final, she didn't have the support of the fans & wouldn't win, so voted her out.
Damsel Scrappy: Katie Waissel may have the biggest hatedom of any contestant ever, yet somehow she kept on getting saved...
Fridge Brilliance: The voting / disqualification system seems unfair. You vote for your favourite and the person with the least number of votes is disqualified. But since the votes are non-transferable you can't vote for your number 2, 3, 4, etc. so a contestant could get disqualified by being everyone's second favourite, while the most hated act could survive if they had a few eccentric voters. But while it's unfair on the contestants it's brilliance on the part of the show itself, as this system forces the best possible performances out of the contestants. i.e. if you want to stay in it, you'll have to rise above the rest in at least some people's opinion, as opposed to allowing them do enough to just not be the worst which could encourage more mediocre performances .
Glurge: Multiple Glurge acts will appear every season, and this is something the series detractors like to home in on. The majority of good acts will often tell their sad backstory on camera and how they absolutely have to win the competition, with equally glurgey music playing in the background. Usually, the sadder the story, the farther they get. Even though some acts actually have talent and don't need to do this.
Adding to the One Direction-related humor, Simon, after the attempt to use Leeds for an audition area (see Epic Fail on the main page), declared Yorkshire a musical wasteland. Two members of One Direction (Louis and Zayn) are from Yorkshire (Doncaster and Bradford, respectively).
Ho Yay: Johnny Robinson and Gary Barlow. So. Very. Much.
Hypocritical Fandom: What's that? The online campaign to get Killing In The Name by Rage Against the Machine to Christmas No. 1 is unfair? Compared to what? The several month long advertising campaign to get the latest winner of a singing contest to Christmas No. 1?
Seasonal Rot: Many see the near-total overhaul of the panel in 2011 as the point where things started to go wrong for the show, with ratings dropping sharply (albeit still being pretty good overall), the show consistently getting beaten in the ratings by Strictly Come Dancing, and the press becoming overwhelmingly hostile toward the show rather than treating it as just a bit of goofy fun. Not to mention, it came off the back of the 2010 series, which was the show's highest rated season and the one that eventually spawned a worldwide musical phenomenon of its own. On top of that, the huge flop of I Can't Sing!, the 2014 musical based on the show, has been treated by many as a sign that the show's popularity is in terminal decline.
So Bad, It's Good: Despite their complete inability to sing, Chico Slimani, Jedward and Wagner all developed fandoms who could appreciate their somewhat unique talents.
Ablisa in the 2010 auditions. Though, that was more to do with the fact that they shouted at the crowd to shut up when they booed and one punched the other in the face.
Subverted with Goldie from the 2011 auditions. She had no ability to sing and largely depended on her stage antics and was surprisingly passed through to Judge's Houses. Louis became her mentor and put her through to the live shows but in a rare case of Genre Savvy, she withdrew from the competition as she suspected she was the token "novelty" act if she continued; she was then replaced by a more competent contestant.
The Scrappy: Every series has an unpopular contestant or two, usually because they get further in the competition than more talented counterparts. However, few contestants are as overwhelmingly disliked as Emily Nakanda and Frankie Cocozza, the only two contestants to date who actually got thrown off the show for behavioural reasons.
The Woobie: Wagner has been getting this, despite being tone deaf and missing notes he has proven to be quite popular, even he is aware of his problems as he apologises to the judges for it. However several scathing comments from fellow contestants and judges have made him more sympathetic to the audience.
Too Sexy For This Timeslot (Khandi Rain from 2009, who were former strippers who wore Stripperiffic outfits. Cheryl Cole and Dannii Minogue criticised them for doing that. While it's certainly true it wasn't helping them move on, getting criticised for Fanservice by someone who posed nude for Playboy is a bit rich)
The show got in trouble again for Christina Aguilera and Rihanna's performances on the 2010 final, both of whom appeared in what appeared to be their underwear and giving performances that were perhaps a tad overly-sexualised for a family audience, at least according to the tabloids.
In the classic British tabloid tradition of "Scenes that are too obscene and immoral to be shown - full pictures with close-ups inside!"
Award Snub: Surprisingly, the X-Factor wasn't nominated for the 2013 Kids' Choice Award for Favorite Reality Show, but Simon Cowell did win "Favorite Villain" - although his win probably was influenced more by his managing of One Direction than his actual role on the show.
From season 2, there is Cece Frey, who was in the bottom 2 in 4 out of 6 live shows, and gets fairly consistent criticism (or compliments based on factors other than singing) from the judges, yet managed to finish in sixth place. Also, after the second time in the bottom, she chewed out the viewers, saying "I gave 110% last week, and you still put me in the bottom", showing a remarkable lack of gratitude for the votes she did get.
Hilarious in Hindsight: LA Reid didn't know the Demi Lovato song "Skyscraper" when Drew sang it. Now that Demi has joined him on the judging panel, this becomes funny.
The Scrappy: Steve Jones, Nicole Scherzinger and for contestants Marcus Canty and possibly Astro
Khloe Kardashian in Season 2, but she was already one before joining the show. Mario Lopez hasn't fared much better.
Tear Jerker: One of Britney Spears' past collaborators, Don Phillips, auditioned for season 2, but was not very good, and was told no by all four judges, including Britney. The worst part was him in tears afterwards. Not because of him getting told no, but because he felt like he had "hurt Britney".