I think it's fair to characterize the overall critical reception of The Avengers: Age of Ultron, bracketing that subsection of critics that self-identify as fanboy geekdom, as ranging from "fine" to "meh." My impression is that this reaction doesn't align with the broader audience's, which is to say, the opinion of people who have chosen to pay money to see the movie. Three features above all have characterized the blasé critical response, at least in what I have read. Although presented as conclusions, they can equally be understood as premises, that is, judgments (however defensible) that critics bring with them to the film.
Premise #1: That the exponentially increasing, seemingly endless glut of superhero movies is (cinematically) undesirable; specifically, that it has resulted in monotonous movies whose predictable patterns are, in the end, simply boring.
Premise #2: That this glut of superhero movies is bad for other movies, because it reduces the film business to pumping out "properties" and "franchises" in a "shared cinematic universe," and crowds out original ideas as well as projects that don't require a $200+ million budget.
Premise #3: That this glut of superhero movies is culturally meaningful, in largely if not entirely negative ways.
Here's what I'd like to say by way of response, as a non-fanboy and comic book non-reader, who has nothing invested in the success of the Marvel Cinematic Universe (MCU) but has, nonetheless, generally enjoyed the films belonging to it so far.
To the first premise: What is at issue, at bottom, is nothing more than a different of taste. One writer described the typical MCU entry as inevitably climaxing in CGI spectacle of the Rock 'Em Sock 'Em variety—a cavalcade of flying, fighting, and explosions, by and between computer creations. The problem is that this is description passing as evaluation: what if one likes CGI spectacle of the Rock 'Em Sock 'Em variety? There's nothing inherent in the form that rules out quality; see Guillermo del Toro's Pacific Rim, which garnered positive reviews from across the critical spectrum. Moreover, to the reply, "But the problem is, I've seen this before," so what? It's not literally the same; and plenty of people like similarity. Critics aren't immune to the comforts of familiarity: witness critics' falling all over themselves to lavish praise on the Fast and Furious franchise, which nobody denies is a surfeit of cliched dialogue, recycled beats, and CGI/stunt car action—churned out because audiences lap it up, and pay money to do so.
None of this is to say that there aren't genuine, substantive criticisms to be made of the MCU films; there are, at multiple levels. The direction tends to be uniform; the action, merely competent; the plot, MacGuffin-centric; the surprises, telegraphed. But in reading the latest round of reviews these kinds of critique don't take center stage. What does is the overall feeling of sheer exhaustion, as if critics had finally reached the point of saying, "More? Really? Of this?" And, looking at the horizon of releases populated by Marvel and other comic book adaptations, reviewers take as their object of commentary, not the film in front of them, but the whole sweep of films and universe-building that has led to this point. And they don't like it.
My response is simple: What if a lot of people do? What if tired dissatisfaction with the very idea of the MCU isn't sufficient as a cinematic judgment about a particular movie? After chatting about Age of Ultron with a friend recently, he shrugged his shoulders and said, "I'm just not interested in that kind of movie." I wonder whether critics could be honest enough to say that, and not contort their reviews into justifying what feels like a predetermined position.
To the second premise: I think this entire line of reasoning is fallacious. On the one hand, there have always been trends in Hollywood studio filmmaking, trends that have prioritized money over ideas, business over art, bureaucrats over creatives. Not only is this latest trend not new, it's not particularly insidious compared to others. On the other hand, it isn't clear to me that it is true, or at least true necessarily. Is it, broadly speaking, stupid that Warner Bros./DC Comics is aping Disney/Marvel's success? Yes. The same goes for Fox with Fantastic Four, Sony with (the now aborted) Amazing Spider-Man, Paramount with Transformers, and others. But that's not a judgment on the wisdom or value of the MCU. Nor does it mean that the MCU's success entails, or must entail, all other studios slavishly imitating it. Nor, finally, does such imitation spell doom for all smaller budget and/or original projects. Blaming the MCU for the recent relative paucity of medium-sized smart adult dramas is lazy thinking. Letting that inform how one assesses particular films is taking that laziness and doubling down on it.
To the third premise: There are important negative things to say about the "meaning," such as it is, of the Marvel movies, not least the almost aggressiveness White Maleness of it all. (Recent announcements of actors playing secondary characters in Captain America: Civil War read like a casting call for Prominent White Character Actors. It recalls the latter seasons of The West Wing: surely at this point it's a prank, and they're trolling critics by refusing to cast persons of color?) But apart from the formal problems with the MCU—problems that are systemic, common to nearly all Hollywood blockbusters, which preceded Marvel's foray into film, and whose absence would not change critics' stated stance—I want to advance what is apparently a radical thesis.
The Marvel movies don't mean anything.
I don't mean they are lacking in meaning. I mean that, analyzed for their cultural value or import, they are basically nil. That goes for positive as well as negative meaning. They don't "say" anything, in part because they don't have anything to say, in part because they don't "reflect" anything "about us," that is, about "who we are today." That people like these movies doesn't say anything about Americans living between 2008 and 2015. If they had been released one, two, three, four decades earlier, they would have been equally popular. They are popular because, at long last, technology and filmmaking have become capable of rendering realistically characters and stories that have, up until now, been limited to the written word, the still image, and animated motion pictures. They are, literally, super, beyond: beyond realism and daily life, beyond the capacity of everything but imagination—until now. So people are flocking to see what the latest feats of cinematic, visionary craft have in store for them.
And they love it.
So, my response to the critical response? A shrug of the shoulders. Age of Ultron was fun: a blockbuster to see on a warm summer night, in a crowded theater, with a bag of popcorn; full of punch lines, gags, and visual punctuation marks; packed to the gills with set piece upon set piece of (not over-, though definitely hyper-)stuffed superhero action. It was neither perfect, nor Great, not full of meaning. It was a well-coordinated, smartly scripted, explosions-full capstone to seven years of set-up. It worked for me, it worked for the crowd I saw it with. I have a feeling its makers hit their intended target.
Unless one is predisposed against thinking so, I think that should be enough.