I've been unusually busy with work lately, so I'm already one of the last people on Earth to see The Avengers – and it's only been out for three weeks. Owing to the movie's incredible popularity, there's not much useful I can add to the conversation, though I will share my opinions.
During its opening minutes, watching the film feels very much like reading one of the old Avengers comic books from the late '70s/early '80s: visually crisp, action-packed, and filled with dialogue that leans a little too much on the hokey side. However, once the various super-powered individuals start being recruited to save Earth from the trickster alien-god Loki and his deadly outer space army, Joss Whedon's work as both writer and director really shines. (He cowrote the story with frequent superhero scribe Zak Penn.)
Marvel Studios itself is owed some credit, as they have shown a sort of genius in choosing directors for their franchises, and have taken pains to slowly compile a well-balanced cast. They've got the cream of the crop with The Avengers, for it's a truly daunting task to round up so many disparate characters – four of whom have already played the lead in their own movies – and give each of them equal time, each of them a solid character arc, while maintaining a tight storyline. But Whedon pulls it off with wit and suspense, bringing in the visual and storytelling styles of each character's earlier film – Iron Man's glibness and romantic edge, Captain America's romanticized patriotism, Thor's Shakespearean bombast, and The Hulk's gritty paranoia – and blending them seamlessly into a cohesive whole. He even makes silly-sounding weapons like a shield, a bow, and a hammer actually look powerful.
Considering the herculean task of pulling off something like The Avengers so well, Whedon can be forgiven if his plot has a few bubbles. (For instance, Captain America seems awfully quick on catching up with advanced 21st Century technology; characters brought under extraterrestrial mind control seem to snap out of it pretty easily; and Loki's mortality/immortality remains constantly in flux. You apparently can't kill the guy, yet he does have bloody cuts after getting his ass kicked. So what's up?) But despite the portentous dialogue at the beginning, and an epilogue of TV interviewees with some of the worst day-player actors I've seen in a while, The Avengers delivers the goods. As you have probably already discovered for yourself.