Zach Baron has mixed feelings about The Avengers:
The Avengers is already a smash. Our reward? Iron Man 3, Thor 2, Captain America 2, and if the obligatory post-credits sequence in Avengers is any indication, Avengers 2. Whedon did something near miraculous, making Avengers into something entertaining. But that is an awful lot of a good thing.
Douthat seconds him. Christopher Orr has fewer reservations:
Now it is true that if you don't like superhero movies, you probably will not like The Avengers, which features all the tropes that inevitably accrue to the genre: the flying and punching and force-beams and silly costumes. But if you are even modestly open to persuasion, Whedon's effort is right up at the top of the Marvel heap, with the first Spider-and Iron Man and the first two X-Men. Given the degree of difficulty inherent in the undertaking, it's an accomplishment only modestly short of a miracle.
Alyssa Rosenberg raves:
The Avengers may be the result of careful planning and a neatly calibrated movie-making formula that strikes some critics as rigid corporate entertainment. But this franchise, with its long-form exploration of a rich cast of characters and its embrace of a huge, complex universe, has unlocked, at long last, the wondrous, weird potential of comic books to transport us to other worlds and to render our own transformed.
The Dish 