Shakespeare's valedictory play comes to the screen with the leading role of Prospero, the ousted Milanese nobleman practising his dark arts on a Mediterranean island, changed to Prospera so that Helen Mirren can play the part. She's predictably splendid - bringing the verse to life, attuned to the rage and compassion in the material - though the gender switch gives the impression that director Julie Taymor's adaptation is a more radical beast than it actually is. True, Ben Whishaw's Ariel is an androgynous, digitally tricked-out sprite, and Djimon Hounsou's presence as the brutish drudge Caliban suggests a Shakespearean critique of colonialism, yet this is an otherwise conventional affair in Elizabethan dress, with rugged island locations. For all Taymor's superficial computer-generated frippery, it works best when she lets her actors simply get on with it, with both shipwrecked aristocrats David Strathairn and Chris Cooper, and their mischief-making crew (Alfred Molina, a surprisingly effective Russell Brand), matching Mirren's accomplishment. The result is certainly good enough to leave us once more astonished by Shakespeare's invention, yet it ultimately lacks the interpretative authority that might have made it something special.