I'm working hard to get my picture book version of Sir Gawaine and the Green Knight finished, since (hurray!) a publisher wants to see it. Two big problems remain. The first is the ever difficult Pale Lady, who I still want to make more dangerous. Haven't gotten to that one yet. The second is the opening.
I've never been happy with page one -- the first 10 or 15 stanzas. They seem both static and contrived. In my fiction, I usually open with people and incident, and let the where-they-are and how-they-got-there and what's-the-trouble fall into place around them. So far, lucky me, it always has. But this time, it's not. The poem doesn't begin to interest me until page 3 or 4.
I tried both the classic openings: "Once upon a time, there was a castle" came out as "In Camelot before the sorrows / shut up snug against the snow / Arthur and his court were feasting / in bright mid-winter, long ago." Pretty (owing much to Rosetti), but as I said, static. Dull. And Gawaine doesn't even come up until page 4.
I tried "Once upon a time, there was a boy" -- the character-driven approach that most modern children's literature uses, though not always wisely. "Gawaine was raised an honest farmboy / of noble blood, though he was poor".... But that just seemed to make the opening longer. I still had to do most of the castle stuff.
My interim solution, while waiting for a blinding flash of insight (Here, muse, muse, muse....) is to make the darn thing as short as possible. But even that seems to be a pacing problem. Argh. Anyway, here's how it goes.
In Camelot before the sorrows
Shut up snug against the snow
Arthur and his knights sat feasting
In bright midwinter, long ago
Among them sat the Gawaine the honest
Youngest, smallest, shy and plain
He'd been raised a simple farmboy
And he had yet to earn his name
Now this was in the Christmas season
When the frost fell thick and deep
When the bells were often ringing
When the bears were fast asleep
On New Years' Eve the hall was merry
With platters going to and fro
With knights and ladies stepping carols
Till midnight bells rang out in snow
And as they rang the hall was shaken
By a knocking at the door
A knock so loud the lintel quivered
And shook the holly to the floor
So the doorguard lifted latches
So the knights and ladies rose
To watch the door as it creaked open
Onto the night of stars and snows

I like it but I do see your comment about the possibly-too-quick pacing. I see two openings: one is to have a verse about some of the more famous knights just before you introduce Gawaine (a tactic which heightens Gawaine's youth and ordinariness), the other is to have a verse fleshing out more of the Christmas season between stanzas three and four -- perhaps with some mention of the magics of Merlin?