I've heard talk that this movie is boring. As a history buff, I would have to disagree. Hellen Mirren is brilliant. Ditto James Cromwell who I last saw in The Longest Yard but more fondly remember him from Star Trek: First Contact.
Other than those two, you probably won't recognize any of the other talent although Michael Sheen, who played the newly elected Tony Blair and who's billing you oddly have to go to page two on IMDB for, was quite impressive as well.
Mrs. Roosh said it was "okay", but I recommend it, especially if you favor historical fiction as this movie is set in the time just after Princess Diana's untimely death.