Alejandro González Iñárritu’s Birdman, which stars Michael Keaton as a one-time superhero movie star (just like Keaton himself), is audacious technically, and so meta it may well blow your mind, but it is also weird, maddening, wearing and exhausting. It is so frantically fast-paced it feels as if you are on a theme-park ride that just won’t stop, or slow down, if only for a minute, so you can take a breather, collect yourself, come up for air.