j-e-f-f-e-r-s said:
Other than snarky one liners, all the Avengers has is spectacle. Like Transformers 3, along with practically every other blockbuster of the last few years, the Avengers will simply convince Hollywood to pour money into expensive CGI tech demos that show yet another city being destroyed by yet another extraterrestrial threat, probably by some sort of machiney looking enemy.
I think you're missing two big points here about what makes The Avengers special and extraordinary.
The first is what you dismiss as 'snarky one-liners', but is much more than that: it's a strong, effective group dynamic - precisely what Whedon specialises in and why he was such a perfect choice for the job. It is very easy to underestimate how difficult it is to write effective scripts with large numbers of equally prominent characters, especially when those characters are all interacting with one another (as opposed to separate or intersecting plot strands).
As Orson Scott Card once pointed out, the number of relationships between characters increases according to the square of the number of characters (or thereabouts), so keeping track of those relationships, especially in the context of an action movie with only limited time available for character development, is a huge challenge. Add to that the issue that all these characters are played by major stars and that is a really impressive achievement.
The second is what you dismiss as 'spectacle', for which I'll refer you back to Bob's review of (IIRC) Transformers 3, where he was talking about the poor editing of action movies. I was watching Quantum of Solace the other day and it struck me again there how plain confusing the action sequences were - a mess of jump cuts, extreme close ups and loud noises that made it almost impossible to keep track of what was happening to who, and meant that really all I was doing was waiting for them to be over so we could get back to the story.
Contrast that with the final battle that takes up the last act of Avengers, or for that matter the sequence aboard the flying fortress in the second act. Consider that each of these contained multiple intersecting stories - we're not talking Return of the Jedi here with three simultaneous but separate stories, but one big battle taking place on multiple fronts simultaneously. Note how often we move from one part of that battle to another, and how well we are kept informed of all the action, and how well-paced it is with each character being given their own role and story beats - even useless Hawkeye.
Again, Whedon pulls this off so smoothly that you don't even notice what an achievement it is, but it really is masterful. If I were awarding Avengers an Oscar, it would be for Best Editing.
So - is it Casablanca? No. Is it a better all-round film than Dark Knight Rises? Not sure. But is it a bigger *achievement* than Dark Knight Rises? Undoubtedly, in my opinion.
(tl;dr: They're really, really *good* snarky one-liners and spectacle)