Alfred Hickling runs down some pros and cons in a column for the Guardian:
People are bound to ask if local theatres may be threatened by an incursion on their patch. I doubt it. What's more likely is that non-theatregoers might find out what they're missing and be tempted to book for the real thing. And as long as the NT Live project is treated as an enhancement of its touring work, not a replacement for it, everyone ought to be happy. What will be interesting to discover is what extent the National Theatre might mimic the Met's presentational style, which itself seems to be modelled on Sky Sports. The Met broadcasts not only take you so close to the action that you can see the singers' tonsils, but also supplement the action with backstage footage and interviews with the cast as they come off the stage. Cinema audiences for the Met's Tristan und Isolde were treated to the bizarre spectacle of a heavily perspiring Deborah Voight being collared in the wings and asked if she could talk us through the Liebestod.