Character Rerailment: In the comics, Gambit's characterization had been changed to a self-loathingAtoner desperate to punish himself for his (morally blameless) role in the Morlock Massacre. This movie, however, reaches back to the character's roots and shows him as a competent, charming, handsome, and relatively low-angst card-sharp who won a Cool Plane in a poker game.
Contested Sequel: For many, it is a Narm-fest which flies in the face of the other movies' continuity (particularly rewriting a lot of back story from X2: X-Men United, the franchise's peak until X-Men: Days of Future Past), ruins both Gambit and Deadpool among other characters, allows a lot of characters to make stupid decisions in the name of advancing the plot, and all for the sake of making another movie centered on Wolverine when the first three were essentially his show, anyway. There are also a number of fans who felt that the film was simply a poor rendering of Wolverine's origins that did not capture the true horror and brutality of what the Weapon X program did to him. For others, the continuity wasn't all that important, Sabretooth was finally given his due with some decent character development, the incorporation of some new mutants was interesting, and the whole thing is a fun action film.
Continuity Lockout: The film could have used footnotes to explain the significance of its story elements. Since the Weapon X scene was so brief, it could have said "To learn more, please read Weapon X by Barry Windsor-Smith."
Director Displacement: In a more retroactive case, the film seems to be mostly associated with screenwriter David Benioff, mostly following the much maligned final season of Game of Thrones, of which Benioff was one of the showrunners, with critics of the season attributing many of the faults of the film to Benioff, though Benioff only wrote early drafts of the script and he wasn't responsible for the most negatively received aspects of the film. Regardless, Benioff seems to have supplanted Gavin Hood in terms of association.
Wade Wilson, pre-experiment. Critics and fans pretty much unanimously praised Ryan Reynolds as Wade, and it was what gained Reynolds a shot in the character's solofilms which were not only Truer to the Text regarding the character, but also smash hits with audiences and critics alike.
Despite his short amount of screentime and differences with the character, Taylor Kitsch's portrayal of Gambit was well received. Kitsch himself requested on countless occasions to be cast again in any other X-Men film, but he wasn't brought back for the oncoming movies.
Foe Yay: Wolverine and Sabretooth have always had a fair amount of Foe Yay that's attracted the eye of shippers, because of the intense, obsessive, vitriolic and ultimately unhealthy rivalry they share. The two mutants being portrayed as brothers in this film didn't put a damper on the pre-existing Logan / Victor ship. In fact, Hugh Jackman and Liev Schreiber's macho, tough guy portrayals of the rival, feral mutants actually increased it. See also Relationship Writing Fumble.
Real world instance: Fans had been clamoring for Gambit to appear in X-Men films since the first one. The public response from the directors and writers was, "If we include him, we want to make him integral to the story. We're not going to just throw him in there because he's popular." Come this film, Gambit is in, fulfilling a minor role which could be handled by any character. It really seems like the studio executives just thought, "Who's a popular character we haven't used yet?"
Wade Wilson is placed as Weapon XI in this film, the successor to Wolverine. Recently released comic book Wolverine & Captain America: Weapon Plus #1 reveals that in fact comic Deadpool is Weapon IX, the precursor to Wolverine.
Wolverine's claws get red-hot due to deflecting optic blasts. Later in the comic event Fear Itself would have Wolverine's claws have a similar appearance due to being enhanced by Asgardian magic, and in Return of Wolverine he receives the ability to heat up his claws as a superpower.
Plenty of reviews claim that basically, the only reason to watch the film is because it has Wolverine kicking ass and a decent Sabretooth.
Many viewers were looking forward to the movie just for having the first live-action version of Deadpool. They... changed their mind when the movie came out. Though Ryan Reynolds as pre-transformation Wade Wilson is unanimously considered a highlight of the film, which eventually resulted inmuch better things.
A retroactive example. For those who loved the Deadpool movies would like to make fun of it by watching it.
"Revenge Painting", referring to an incident involving former Fox CEO Tom Rothman re-painting a set behind director Gavin Hood's back, is a term used to describe the copious amounts of Executive Meddling that went into the film.
Mis-blamed: In the wake of Game of Thrones's finale, many people love to use this movie (and Troy to a lesser extend) to show that David Benioff has always been a bad writer. The truth of the matter was that the movie was the victim of Executive Meddling. The original draft by Benioff doesn't have Deadpool to begin with, and neither him or the other writer, Skip Woods, ever had the intention to make Deadpool as Weapon XI. Finally, the decision to have Deadpool's mouth sewn was from Tom Rothman, the president and CEO of Fox at the time, who hated the character.
Narm: Hydrochlorothiazide is mentioned as a drug that was used to slow down the heart rate. However, medical professionals would probably start laughing uncontrollably because that drug is used as a diuretic!
No Problem with Licensed Games: While not a brilliant game, the video game of the movie is a fun, gory hack-and-slash with well-working gameplay mechanics, plenty of fanservice, and expanded plot points. In fact, the game seems to be more well-received than the movie it's based on! (As the developers worked on the also-very-well-received X-Men Legends, Marvel Ultimate Alliance, the two most recent titles in the Star Wars Dark Forces Saga and Star Trek: Elite Force, this may not actually be surprising.) Ironically, the story of the game works rather well when it's not trying to follow the plot of the movie. Interestingly, it also ends on a cliffhanger/possible sequel hook that is completely unrelated to the film's plot. Ironically, though, it sets up X-Men: Days of Future Past fairly well except for the future Continuity Snarl that is Trask.
Patrick Stewarts cameo near the end elicited applause from some theater audiences.
Practically everyone agrees on the sheer awesomeness of the opening credits scene featuring Logan and Victor fighting throughout the wars.
Relationship Writing Fumble: The film is mostly about a heterosexual relationship, but the relationship between Wolverine and Sabretooth is too strong to be unintentional. While both characters repeatedly talk about how they're 'brothers', the constant Something Else Also Rises, playful flirting, eyeing each other, phallic symbolism, and grappling each other while yelling "Feels good, doesn't it?" kind of ruins the 'brothers' vibe. It's worth noting that the comic-book version of Wolverine's childhood featured a significant redhead named Rose as his first love interest. The first scenes in the movie are copied almost directly from the comic, except with a young Sabretooth in Rose's place.
Retroactive Recognition: Runs into issues with the above, of the "How the heck did Troye Sivan grow up to that?" variety.
Scapegoat Creator: An unusual instance of someone achieving this status a decade after the work was released. At the time of the film's initial release, the blame for the underwhelming quality of the end product generally tended to be placed on the executives at 20th Century Fox, as the stories of their Executive Meddling in the production of X-Men: The Last Stand were already widely known, and more stories about their treatment of director Gavin Hood had been circulated just before release. Following the infamously poorly-received finale of Game of Thrones, however, many seem to have decided that the movie's poor quality really was the fault of co-writer (and Game of Thrones co-creator) David Benioff after all, even though he only wrote the earlier drafts of the movie, which were said to be a much darker and more viscerally violent affair.
The effect used to depict Emma Frost's diamond form pops out for its low quality, looking more like little paper flakes than actual diamonds.
Though Wolverine's bone claws are well done, his adamantium claws, particularly in the bathroom scene, inspired much derisive audience laughter. You'd think in a movie explicitly about a mutant with metallic claws, that would get more CGI attention than anything, especially when incarnations in previous films (by the same FX studio, even!) were pretty good quality.
Much of the Wolverine vs. Weapon XI fight is quite obviously shot on a green screen in many shots.
Squick: Wade Wilson's mouth being sewn shut, effectively rendering him the Merc with No Mouth. It's just as unnerving to look at as one might think.
Wade Wilson/Deadpool. After getting the chance to display a weary snarky persona, he's taken out of the film until the climax, where we see that Stryker has basically turned him into an Humanoid Abomination. His mouth being sown shut essentially robbing him of the sole trait he had in the movie.
Speaking of which, in regards to Weapon XI, while it's almost a universal opinion that he's possibly the worst adaptation of a comic character to date, a fair few fans thought he could have been interesting if he was an entirely original character without the name "Deadpool" slapped onto him.
Comic fans had been calling for Gambit to show up in the movies since the first X-Men film. When he finally does here he's little more than a built-up throwaway gag.
They Wasted a Perfectly Good Plot: So we have the opening scene, which establishes that Logan is indeed older than he appears to be, having been born in the 1800s. So no doubt the movie will take advantage of this immortality-based storytelling device and make the movie about Logan's life leading up to the implantation of his adamantium skeleton, right? Nah, let's just relegate that potentially interesting story into a three minute opening credit sequence in favor of a plot that will ultimately become irrelevant due to the inevitable amnesia Logan will suffer from.
To expand, in the opening scene we're shown Wolverine and Sabertooth fighting side-by-side in the American Civil War, World Wars I & II, and Vietnam. Any of those would have made interesting movies and they're relegated to a 10 minutes sequence.
Took the Bad Film Seriously: Just about everyone did this. Ryan Reynolds and Liev Schreiber in particular stand out, making the most of their roles as Wade Wilson and Sabretooth respectively. Reynolds's performance even got him his own, much better-received spinoff franchise.
Uncanny Valley: The film features a cameo of Professor Xavier, which uses CGI to de-age him. The problem is, it's less-than-spectacular CGI and it just succeeds in making him look really creepy—kinda like Humpty Dumpty. The same effect was used in X-Men: The Last Stand to de-age both Xavier and Magneto, but was much better-looking and a lot more convincing.
What an Idiot!: Okay, Wraith. Try to take Sabretooth on. Never mind the fact you're trying to punch a man with an absurd Healing Factor to death. Sabretooth getting a One-Hit Kill was probably a mercy because every punch Wraith landed probably would be doing more damage to himself.
Agent Zero is sent to take out Wolverine, discovering that he's been taken in by a couple, and decides to kill the couple as well if only so he leaves no witnesses - armed with a sniper rifle and in possession of the means to blow up the barn. You'd expect: Him to blow up the barn first, and then shoot any survivors. Instead:He opts to shoot the Hudsons first, and then blows up the barn. Result:Logan now has enough time to escape, and the ensuing chase scene ends with Logan blowing up Zero.
Complete Monster (PlayStation 2 & Wii version): Colonel William Stryker is a high-ranking officer within the US Army and the head of the Weapon X project. Having assembled the team of mutants in the past, Stryker uses them to complete his own personal operations, at one point ordering them to massacre a militia within an African village, and then tries to torture information from innocent civilians there about the adamantium that located within the area. When Logan rebelled against him, Stryker knocked him out and then tried to obliterate the village with a nuke. In the present, manipulating Logan to become his subject in the Weapon X program, Stryker experiments on countless humans, transforming them into his mindless brutes who suffer so much that they thank Logan for killing them.