I probably should not say that this is a movie about middle-aged people for middle-aged people, but it is, and I mean it as a compliment. I certainly can't think of a better historical movie of this sort.
I'd say that it's matched by Goldman's other film on a similar theme, The Lion in Winter, in which a creaky Henry II deals with aging, his estranged wife, bickering adult children and other midlife issues.
One of the minor joys of that movie is William Marshal as a secondary character. He's the one who knows that you should always be waiting outside in the corridor with a drawn sword any time you send the guards into a room to fetch Richard.