I've been to see The Queen.
Helen Mirren is dour and spectacular as Elizabeth II, and James Cromwell is absolutely believable as Prince Philip. Sylvia Syms and Alex Jennings are less physically believable as the Queen Mother and Charles, respectively, but certainly capture the essence of their parts. If Helen McCrory's portrayal of Cherie Blair is true to life, then I must say the PM's wife is not very likeable.
Michael Sheen is Tony Blair - and I mean he is Blair. His lips were a shade too red, but otherwise Sheen embodies Blair as the young, optimistic, charismatic PM who has to drag the royals into the modern era, while maintaining a veneer of protocol at all times.
The movie is convincingly cut with television clips from the time - i.e., Diana's death in 1997 - and for me, part of the appeal of the film is reliving the emotions and events. It's hard to believe that this August will be the tenth anniversary of her death, and the intervening time has given us enough perspective to see just how massive was the reaction to her death.
I think that at the time, many people felt Diana's death and the subsequent reaction, both on the part of the royal family and that of the public, were defining - and redefining - moments for the monarchy. A decade later, however, not all that much has changed. The last few lines of the movie are thus prophetic, not only because Blair reassures the Queen that she and "the institution" will survive the anti-royal backlash that coloured the public sentiment in the first few days after Diana's death, but also because she warns him that one day, the public won't love him so unconditionally, either.
Above all, the movie showed a human side to the monarchy, and convincingly portrayed Elizabeth as a woman with a sense of humour. Also, it was kind of like watching The West Wing with nicer accents. Definite recommendation.
Oh, and in passing, if you haven't seen Stranger than Fiction, rent it. It's great.