steepholm has crystallised the problem for me. The production allowed Simon Russell Beale as Falstaff to dominate proceedings, which fundamentally unbalanced the play; it became a star vehicle rather than a historical drama. He is a powerful actor, and is good here; I was blown away by his Leontes in The Winter's Tale which I was lucky enough to see on stage a few years ago, but genius sometimes needs discipline as well.
Of the other leads, a lot of Hotspur's material was cut (I think two or three entire scenes from Act 4), though I actually felt that Joe Armstrong was more impressive in the role than either Tom Hiddleston as Prince Hal or the curiously subdued Jeremy Irons as the King. (And it was a nice touch to cast Armstrong's real father Alun as his stage father Northumberland.) Michelle Dockery seemed to be phoning in her lines as Lady Hotspur much as she did in Hogfather. Let's hope for better luck next weekend with H4P2.
Incidentally we watched the first ever episode of Black Adder last night with young F, who tolerated us explaining the Shakespeare jokes to him. It was first broadcast 29 years ago.