Thank you all for a great discussion. One last comment on Act 3 . . .

I get a sense that Richard abdicates as much as Henry usurps. As Jetsam points out, it is perplexing how the King behaves. He seems to lose faith so quickly that even those around him are confounded. I think you're right that the story really hinges on these few scenes where the King essentially gives up.

There's another speech that I think shows precisely where Richard loses faith . . . just after finding out that Bushy and Green have been executed, and Lord Scroope tells the King that the common people now recognize Bolingbroke as lord. This is where Richard uses the term "Hollow Crown”—the title of the BBC production that spans events in the four plays of the Henriad. He also talks much of death as he does later in scene 2.

KING RICHARD II

No matter where; of comfort no man speak:
Let's talk of graves, of worms, and epitaphs;
Make dust our paper and with rainy eyes
Write sorrow on the bosom of the earth,
Let's choose executors and talk of wills:
And yet not so, for what can we bequeath
Save our deposed bodies to the ground?
Our lands, our lives and all are Bolingbroke's,
And nothing can we call our own but death
And that small model of the barren earth
Which serves as paste and cover to our bones.
For God's sake, let us sit upon the ground
And tell sad stories of the death of kings;
How some have been deposed; some slain in war,
Some haunted by the ghosts they have deposed;
Some poison'd by their wives: some sleeping kill'd;
All murder'd: for within the hollow crown
That rounds the mortal temples of a king
Keeps Death his court and there the antic sits,
Scoffing his state and grinning at his pomp,
Allowing him a breath, a little scene,
To monarchize, be fear'd and kill with looks,
Infusing him with self and vain conceit,
As if this flesh which walls about our life,
Were brass impregnable, and humour'd thus
Comes at the last and with a little pin
Bores through his castle wall, and farewell king!
Cover your heads and mock not flesh and blood
With solemn reverence: throw away respect,
Tradition, form and ceremonious duty,
For you have but mistook me all this while:
I live with bread like you, feel want,
Taste grief, need friends: subjected thus,
How can you say to me, I am a king?
Act 3.1

The above line stands out for me after reading Act 4 . . .
Tradition, form and ceremonious duty,
For you have but mistook me all this while:

There’s a phrase—all form, no substance—and I think Richard II’s reign has been like that. The patina of king washes off in this scene, even before he finds that York has “join’d with Bolingbroke” (which isn’t quite true).

After finishing the play, I would say the climax is here in Act 3. The rest of the play is all a bit of housekeeping and setting the stage for Henry IV, Part 1.