Considering that the film is about a team of superheroes fighting an alien army, The Avengers is a surprisingly funny film. Although Tony Stark was always amusing, the other Marvel heroes are given a chance to shine, with a witty script that includes great one-liners and numerous references to the characters' odd backgrounds.
From Captain America recognizing a Wizard of Oz reference, to Black Widow's comments about the climactic battle, the smart script uses levity and humor to keep the story humming even when the action has slowed down. A far cry from the more serious (too serious?) tone of Chris Nolan's Batman movies.