Ever since Samuel L. Jackson poked his eye-patched head in for the post-credits stinger in “Iron Man,” audiences have been looking forward to the inevitable “Avengers” movie. In creating this film, Marvel Studios had to launch four separate franchises and establish four superheroes worth caring about in the process. One misstep, and it could have been a disaster. Not only did they do it, they absolutely nailed it. “The Avengers” is the best film in the Marvel canon, a massively entertaining summer blockbuster and a huge success for writer/director Joss Whedon.

Thanks to their respective setup films, we already know Tony Stark/Iron Man (Robert Downey Jr.), Steve Rogers/Captain America (Chris Evans), Thor (Chris Hemsworth) and Bruce Banner/Hulk (Mark Ruffalo). It would be easy to say Whedon had all the tough work done for him since each of these heroes was established in their own film (or two), but juggling these big, distinct personalities could have been an equally foreboding challenge. Whedon doesn’t disappoint, and he crafts a true ensemble, even as each character gets his own big moment.

Each of the films preceding “The Avengers” had its own issues, but if there’s one thing Marvel has done right on a consistent basis, it’s casting. Chris Hemsworth has had a great month between this and the Whedon-scripted “The Cabin in the Woods,” and his Thor is much more layered and interesting as he is forced to battle with his brother, the nefarious Loki (Tom Hiddleston). Hiddleston is fantastic here, full of anger and insecurity, and his chemistry with Hemsworth gives the film’s conflict an emotional complexity that many comic book good vs. evil stories lack.

Evans and Downey are the characters who chafe the most often as Captain America’s unflappable optimism clashes with Iron Man’s shielded cynicism, and “The Avengers” is smart in the way it incorporates Tony Stark’s daddy issues into their relationship. Evans continues to impress as Steve Rogers is relocated to a time period he doesn’t understand, and Downey’s Tony Stark comes so naturally at this point that it’s impossible to discuss the character without thinking of his portrayal.

The only major cast member who didn’t get a chance to establish himself in a previous film is Mark Ruffalo, but he’s a perfect fit for Bruce Banner, and the Hulk ultimately ends up walking away with the movie. Ruffalo plays Banner not as an emotionally conflicted scientist, but as a man who’s come to terms with his unusual condition. When the Hulk finally comes out, it’s equal parts inevitable descent into madness and joyous celebration of destruction, and many of the best beats in Whedon’s sprawling Manhattan climax focus on the green force of nature..

For “The Avengers” to work, Marvel needed not only someone who could write well for its heroes, but someone who could deliver action scenes on a massive scale, and Joss Whedon turns out to be the perfect man for the job. His setup is quick and easy, and starting with the opening assault on a military base, Whedon stages his action scenes with incredible scope. From there, he just goes bigger and bigger, while never losing sight of his characters and infusing the most intense moments with a sharp sense of humor.

The film’s final action set piece, a sprawling alien invasion in Manhattan, is a climax in the truest sense of the word. Whedon finds a way to pay off character dynamics that have been simmering the entire film while staging one of the most impressive, massive action scenes to hit screens in far too long. Imagine the epic final battle in “Transformers: Dark of the Moon,” but this time, you actually care about the characters, and you have an idea of how insanely exciting and satisfying “The Avengers” is.

“The Avengers” is the event movie that every summer blockbuster wishes it could be, the final result of a grand, multi-franchise experiment that works better than anyone ever dreamed it could. Thanks to Joss Whedon, the strong cast and the undeniably smart people pulling the strings at Marvel, “The Avengers” is a resounding success and a wonderful start to what promises to be an unforgettable summer of movies.

Printed on Thursday, May 3, 2012 as: 'Avengers' blasts off with solid cast, staging