Do you have a sore rear? You may be suffering from superhero fatigue

Have your eyes become overly sensitive to bright colours? Is there a persistent ringing in your ears? Do you have a sore rear from too much time spent on the edge of your seat? Then perhaps you're suffering from superhero fatigue. And no, that's not what happens to the Hulk when he shrinks back into a shuddering Bruce Banner. It's what some audiences seem likely to experience after two-and-a-half hours in the dark with Avengers: Age of Ultron.

Several critics have self-diagnosed the condition after enduring Marvel's latest blockbuster, and I too exhibited some of its symptoms last week, when I slipped into a matinee screening in LA. I say that as someone who sat through all nine of the previous Marvel movies necessary to fully appreciate the entire Avengers backstory (10 if you count Guardians of the Galaxy), and enjoyed them all – Thor: The Dark World notwithstanding.

Whether the rest of Marvel's audience is experiencing the same sense of exhaustion is unclear, given that A:AOU enjoyed the second-biggest opening in US box office history, with $191m – beaten only by its predecessor, which earned $207m in its first weekend. Remarkable, isn't it, how the second-biggest opening gross of all time can be framed as a disappointment when you live in the Marvel Cinematic Universe (MCU).

Does that dip mean the genre's profit potential has peaked, or simply that a lot of people decided to stay home and watch the Mayweather vs Pacquiao fight? We'll see whether the trend continues in 2018 and 2019, when receipts come in for the third and fourth Avengers movies.

It's not that A:AOU is of lesser quality than its predecessors; it's somewhere in the middle. But as I watched, the full implications of Marvel's success began to sink in. This is the studio's first release since unveiling its slate of at least 10 forthcoming films stretching to the end of 2019. Some reports suggest the company has scheduled as far ahead as 2028.

Most of the major characters in it have survived on the page since the early 1960s. And if the films intend to mimic their comic book origins, who's to say those characters need ever die, or even reach anything resembling a natural narrative conclusion? With the rare exception of Christopher Nolan's Batman trilogy, every superhero movie must, for commercial purposes, be sequel-ready.

Marvel recently expanded into TV, with the shows including Daredevil, the most popular new show on Netflix. Yet its movies have also come to resemble a TV show, albeit with a blockbuster effects budget. Just as every episode of Columbo ended with "just one more thing," so every final act of an MCU film finds our heroes rescuing the Earth from certain destruction, and reclaiming a MacGuffin from the clutches of a supervillain.

Tony Stark is the MCU's Tony Soprano, its flawed antihero. Thor is to the Avengers what Joey was to Friends. Chris Evans, who plays Captain America, is committed to the character for three more films, including the second Captain America sequel, which is shooting this summer, and the next two Avengers instalments, to be shot back-to-back starting next year. That sounds more like a soap opera gig than a superhero.

I watched the first couple of episodes of Daredevil, and then gave up before I could get in too deep. I may have to quit coughing up for the movies before 2028, too, by which time I'll be well into middle age. As long as the superhero bubble remains this wildly profitable, there's little danger of it bursting. But even for fans, the Marvel movie-going experience is at risk of becoming more an obligation than a pleasure.

Tim Walker is the Independent's LA correspondent