[...] Birdman is a departure for director Alejandro Gonzalez Iñárritu, best known for the heavy dramas Babel, 21 Grams and Biutiful. No trivial satire of Keaton's career as the first and best Batman, it concerns the torments of a career in the arts - the awfulness of contending with other egos, hostile critics and a loony public. In his previous movies, Iñárritu has attempted stories on a grand scale, but he has been at his best, as in "Biutiful," in conveying flights of the spirit, the journey of a single consciousness colliding with the world. [...] we get the crazy new world of celebrity, too, in which, once famous, you remain famous, even if you're washed up; and in which a trending video of yourself running down the street in your underwear - something that in another era might mean humiliation - constitutes "power." In an inspired bit of casting, Zach Galifianakis plays the business manager, a fretting business manager - a mostly dramatic role but one that benefits from Galifianakis' abandon and timing. [...] principally, there's Keaton - weathered and full of doubt, someone life has rendered too human for superhero antics, and yet at the peak of his real and important power, his power as an actor.