I'll hardline on this: the less a Shakespeare adaptation adheres to the text, the better it is. If Michael Bay had claimed Armageddon was an adaptation of Cymbeline it would have been a perfect movie. And no one knows Cymbeline so he'd have gotten away with it!
Ok that may not be true, but when Akira Kurosawa adapted Macbeth via Noh theater and his normal feudal Japan setting he created a masterpiece. Throne of Blood (1957) may not be the most literal translation of the Scottish play, but it is hands down the best film version. I'll go to the mat for that.