However questionable an idea it may have seemed initially, and at times along the way, Marvel's cinematic master plan for its comicbook all-stars pays off in extravagant fashion with "The Avengers." Like a superior, state-of-the-art model built from reconstituted parts, Joss Whedon's buoyant, witty and robustly entertaining superhero smash-up is escapism of a sophisticated order, boasting a tonal assurance and rich reserves of humor that offset the potentially lumbering and unavoidably formulaic aspects of this 143-minute team-origin story. With fan-ticipation reaching Hulk pressure-cooker levels, Disney's domestic and international returns will be nothing short of stratospheric, ancillary streams close to eternal."The Avengers" fully keeps the promise implicit in that plea, taking one of the dominant movie trends of recent years -- the nonstop proliferation of comicbook-based superheroes -- and pushing it to orgiastic new levels of CG-inflated, 3D-augmented geek-out mayhem. Expensive and expansive though it may be, however, the film is no bloated behemoth. As written and directed by the ever genre-savvy Whedon, it's a clean-burning, six-cylinder entertainment that exudes discipline in every particular, from the script's balance of sincerity and self-effacing humor to the well-integrated visual effects to the keen sense of proportion that governs the ensemble. Whenever the possibility of boredom or excess rears its head, Whedon finds an elegant solution.