A lot of the criticisms of the Marvel Cinematic Universe date back to the earlier films in the franchise.
- Some of the Phase 2 films, particularly Iron Man 3, Thor: The Dark World, and Avengers: Age of Ultron, were criticized for having too many jokes and Mood Whiplash moments. Iron Man and The Avengers, two well-regarded films in the franchise, both had a lot of jokes, but there was a better balance of seriousness and levity.
- The Avengers is accused of the "too many characters" problem that plagued some of the later films. It's less noticeable because the Avengers all had a common goal and the film itself had a fairly streamlined plot, which was helped by the fact that most of the key characters were already well-developed thanks to previous films. Meanwhile, later movies made the mistake of trying to give every character their own arc and storyline.
- Some people complain about Iron Man getting Wolverine Publicity as more or less the most prominent Avenger (unlike the comics where it's Captain America) and the closest thing the MCU has to a main character. In Phase 1 he was especially prominent after his first movie started it all. He was the first hero to ever headline two movies (Iron Man and Iron Man 2) in a single phase. His cameo in The Incredible Hulk was the first sign of the shared movie universe truly getting into gear. He was indirectly linked to Captain America's origin story (and later SHIELD's as well) through his father Howard, and finally Stark Tower played a major role in the climax of The Avengers. While a few grumbled about him being the Face of the Band for The Avengers instead of the traditional leader Cap, most fans accepted his increased role at that time since Iron Man was fairly new to the public and Robert Downey Jr.'s snarky comeback performance was unique for superhero movies. However, most complaints about Tony Stark's Wolverine Publicity really began with Age of Ultron, where he replaced Ant-Man as Ultron's creator though this was due to then-director Edgar Wright tying up the Ant-Man characters in their own movie which was stuck in Development Hell for Phases 1 and 2. Then Tony went on to become a co-lead in Cap's third movie and went on to mentor Peter Parker/Spider-Man, more or less replacing Uncle Ben, which ticked off more fans. Even his death didn't stop this, as Mysterio's motivations in Spider-Man: Far From Home were tied to Stark's actions.
- The complaints of the fans had about Tony usurping Uncle Ben in Spider-Man: Homecoming and Spider-Man's own great supporting cast and rogues gallery tied to his rather than stand on its own, can also be traced to Age of Ultron, where Tony usurps Hank Pym's status as the creator of Ultron and his entire character arc as The Friend Nobody Likes of the Avengers. This was criticized then at the time, at least by Hank Pym and Avengers fans, but most audiences outside that group were fine with these changes and were welcoming of them. When Ant-Man came around, some early critics came around and admitted that giving the blame of Ultron and the baggage associated with it to Tony allowed MCU Hank Pym to escape the major toxic reputation that his comics' counterpart had earned. This Wolverine Publicity and Character Shilling however became divisive with Homecoming because Spider-Man is more iconic and famous than Ant-Man, and his origins and supporting cast had been adapted previously into iconic and classic films, and where Ant-Man and Iron Man in the comics are known for having a weak supporting cast and rogues gallery, Spider-Man is considered to have some of the best versions of either category, and many felt that shoehorning Iron Man and Happy into Spider-Man's corner came off as disrespectful, with Iron Man seen as taking Spidey's thunder.note
- The later movies, especially in Phase 2, are often criticized for having flat, one-note villains like Malekith and Ronan the Accuser. This is likely because Loki wound up becoming a Breakout Villain in Thor and (to a greater extent) The Avengers (2012) by having depth and dimension; prior to that, none of the villains (Obadiah Stane, Abomination, Ivan Vanko, and the Red Skull) were all that memorable. Following Loki's popularity, however, audiences were far less tolerant of generic villainy, especially considering that Serial Escalation made the stakes so ludicrously high that there was no way they could succeed. It should be noted that audiences tolerated the weak villains in Phase 1 because it was seen as an acceptable trade-off for focusing on the introductory character arcs of the heroes; by Phase 2 when the hero arcs become less important, fans were less willing to overlook the weaker villains. This would be corrected by Phase 3 films such as Spider-Man: Homecoming and Black Panther that eventually provided villains with substance, if the positive critical response to them is anything to go by.
- The overabundance of Spinoff Hooks has become a problem that has taken over the MCU and spread beyond to other franchises. This goes back to the very first Iron Man movie with Nick Fury showing up to tease The Avengers during The Stinger. This was pretty surprising and groundbreaking at the time, but it was purely a bonus scene tacked on after the credits that had little bearing on what came before; Iron Man still worked as a standalone movie without it. Now, a common complaint about Hollywood blockbusters in general (not just Marvel's films or even superhero films) concerns how the films go out of their way to advertise future installments and spinoffs instead of building cohesive stories, leading to unresolved plot threads that harm the narrative and turn off audiences just for the sake of a hook, which can become even worse if the proposed spinoff in question ends up not happening.
- Most viewers agree that The Avengers marked the franchise's Growing the Beard moment, but it was also the start of its problems with Continuity Lockout, which ultimately became one of its most criticized aspects. The movie generated a lot of buzz because it finally featured the long-awaited team-up between Iron Man, Captain America, Thor, and the Hulk, but it also built on several plot points introduced in the characters' previous solo movies, making it somewhat alienating to people who hadn't seen the five movies that came before it. Still, it helped that the plot remained fairly easy to summarize ("Thor's vengeful stepbrother strikes deal with alien warlord to conquer Earth, steals mysterious alien artifact from the government to fuel his Evil Plan, SHIELD assembles superhero team to stop him"), and that the previous movies were at least standalone stories that required no introduction.
This isn't so much the case with later crossover films. The sequel Avengers: Age of Ultron can be legitimately confusing if you didn't see Captain America: The Winter Soldier before it; if you didn't, you probably won't understand why the Avengers are hunting HYDRA, why SHIELD no longer exists, or why Nick Fury is in hiding. And if you didn't see Age of Ultron, Captain America: Civil War can be similarly confusing since that movie introduced the characters of Vision and Scarlet Witch, along with the nations of Sokovia and Wakanda—all of which are crucial to the plot of Civil War. In fact, Civil War was so reliant on plot points introduced in Age of Ultron that some fans nicknamed it "The Avengers 2.5". The problem only grew worse with Thor: Ragnarok, which builds off of plot points and development from not only Thor: The Dark World, but also from Avengers: Age of Ultron and Doctor Strange, and consequently requires viewing of all of their prerequisites as well. Avengers: Infinity War added the Guardians of the Galaxy to the mix, gave Black Panther and Spider-Man larger roles, and starts the action from The Stinger of Thor: Ragnarok, meaning you will have to have seen all of those films and their prerequisites (including, yes, Civil War and its prerequisites).
- For a close-knit team of superheroes, the Avengers seem to spend an awful lot of time fighting each other. In later years, this has become one of the biggest criticisms of the MCU, with some critics suggesting that it's an attempt at making up for the fact that few of the actual villains are particularly interesting. The problem can actually be traced back to The Avengers, when the heroes spent roughly half of the movie squabbling and fighting before putting aside their differences to fight Loki. But it was easier to tolerate there, since the squabbling was actually done for Character Development: it established the Avengers as a group as mismatched people with very different philosophies and personalities, and it made it all the more cathartic when they learned to work together. This wasn't quite the case in Avengers: Age of Ultron and Captain America: Civil War, when the heroes went right back to pummeling each other—with increasingly flimsy justifications. By Civil War, many fans felt that the hero-on-hero action had gotten out of hand. Civil War has this as its main draw, so many hoped it would be the end, but in Avengers: Infinity War, an unnecessary and plot-slowing fight between the Avengers and the Guardians of the Galaxy showed Marvel isn't giving up on this.
- Within a similar vein, a constant sub-plot about lack of trust between the heroes leading to some kind of complication (at best yelling, at worst full-on internal warfare) that allows the villains to constantly advance their plot until the climax finally hits, everybody accepts to at least try to trust the others for the sake of saving the world... and then things get back to square one by the next movie/season, with a potential for the yelling and warfare to become even worse. This situation was set all the way back to the very first Iron Man with Tony going behind everybody's backs to try to correct what he felt was his greatest mistake that was the Ten Rings running around with his weapons, then it hit one of its big snags on The Avengers with Tony and Steve confronting Nick Fury about creating weapons based on HYDRA (and Stark) designs to supplement SHIELD's (by Fury's words) "laughably useless" firepower against enemies like Loki (although then it was the payoff of such things like the Tesseract). By the time of several seasons of Agents of S.H.I.E.L.D. and Captain America: Civil War, though, this lack of trust had become truly infuriating and the fact that it was highly important to the interaction between Tony and Peter on Spider-Man: Homecoming (which itself made Tony even more of a Base-Breaking Character) has had more than one person say that this type of plot has about overstayed its welcome.
- When Marvel first announced they were expanding to the television format in 2013, it was widely embraced by the fanbase for a variety of reasons. It would allow the world of the MCU to expand beyond just what the movies could show, characters who were unlikely to get into a film could get their dues somewhere else, and the possibility of very real crossovers would be a dream come true. The issue is that the television side was handled by the aptly-named Marvel Television, under the lead of the widely-maligned Ike Perlmutter, who MCU architect Kevin Feige publicly disputed with and nearly quit because of, until Marvel Studios was reshuffled to be a direct Disney subsidiary instead of one to Marvel Entertainment. This meant that there was effectively zero chance of crossover, even if Feige wanted to bring them in as they have different rights, and the result is that all the shows were officially part of the MCU despite being in no way connected to it outside of brand. As such, the idea of a character being big in a Marvel TV show was seen less of a blessing and more of a death sentence, because they would be trapped in the Expanded Universe and unable to be used to the main movies (as that counted as being in the MCU even still). This, ironically enough, made the endless possibilities that the TV side of Marvel hyped as feel a lot more limited instead. For the ultimate proof, look no further than Phil Coulson, the original Breakout Character who headlined Agents of S.H.I.E.L.D.. In the movies, he hasn't been referenced once and you would likely still think he's dead, despite the show making it clear he was revived. Clark Gregg's commitment to the show meant he could never return to the movies (outside of a small role in Captain Marvel (2019), a film set before all of his existing film appearances at that point), despite many fans wanting him to (the show ultimately killed him off again in season 5, ensuring he could never meet the other Avengers again, Gregg's presence in the show now is through flashbacks and an evil doppelganger named Sarge). From there, the disconnect only grew, as the shows themselves stopped bothering with trying to reference the MCU and began to act like an Alternate Continuity despite the promise of "It's all connected".
In 2018 and 2019, this finally came to a breaking point. First, as parent company Disney prepped their own premium streaming service Disney+, all the shows on Netflix (Daredevil (2015), Jessica Jones, Luke Cage (2016), Iron Fist (2017) and The Punisher (2017)) were all cancelled one after another, as Netflix didn't want to promote their rival platform. Second, Disney and Marvel announced that Disney+ would feature series starring characters from the movies such as Loki, Scarlet Witch, Vision, Falcon, Winter Soldier and Hawkeye, all of whom are well-liked movie characters that fans were happy to see more of, with the promise that this is only the beginning, and they're directly seen not by Marvel TV, but Marvel Studios and produced by Feige himself. He alluded to the disconnect in the past, and promised these shows are fully integrated into the universe and will have a symbiotic relationship that will truly expand the scope of the MCU, just as the original series were hyped to do. Third, Agents of S.H.I.E.L.D. sixth season was made without anyone informed of the five-year Time Skip between Infinity War and Endgame, creating a Continuity Snarl so massive that the only way for it make sense is that it's an Alternate Continuity, and Agents itself would announced that its seventh season would be its last. Once having been seen as a viable extension of the MCU, it's now more commonly seen as a void that, while it had good works, only hindered the MCU on a large scale. Many now have completely accepted the idea that the Marvel TV shows, with the possible exception of Agent Carter (the only show produced by Feige, and Jarvis had an unexpected cameo in Endgame), were never canon to begin with and were only promoted as such for marketing reasons. Many of them are fond of the idea of the various properties getting proper reboots in the MCU, while officially denouncing all previous shows as non-canon Expanded Universe much like what Star Wars did to the Star Wars Legends brand.