A few general thoughts concerning this play.
Firstly, it's the third good piece of writing I've seen in London in the last month or so, following on from Apologia and Pornography. Which must be some kind of a record.
Secondly, have been musing since watching it on Monday whether it isn't a closetly intellectual piece of writing. This said because many of the main tenets of conventional dramatic storytelling aren't really adhered to. Byron doesn't go on much of a journey; he starts as a ribald Falstaffian figure and ends as a ribald, bloodied Falstaffian figure, albeit one moved to rage by his enemies. In a more conventional dramatic text (using the phrase in inverted commas), the interaction of the characters leads to some kind of learning, and whilst one or two of Byron's rats make half-hearted discoveries about themselves, they're still more interested in securing some whizz. In essence, the play functions as a manifesto for Byron's hedonistic Englishness. Rylance's performance is impressive, lending the old soak a demented gravitas, and his (and Butterworth's) vision of some kind of primordial Englishness emerges through a mixture of humour and grandiloquence.
Thirdly, the play, steeped in its Shakesperianism, reminds us of things that sometimes get forgotten. (In an era when scripts can almost be put together using spreadsheets.) Monsters make for great theatre (Byron also probably owes a debt to Tamburlaine). Theatre is about putting on a show, rather than education. Showmen put on the best shows, and a dash of lunacy doesn't go amiss either. In fact, in Jerusalem's genealogy, Marlowe plays as big a role as Shakespeare. The character who can unleash language, and play with it like a rapier or a rubik's cube, who can make language sit up and talk... That's a character people will always want to see, a writer people will always want to listen to.
I have only a vague idea of what Butterworth and Byron's Englishness truly represents - the manifesto wasn't altogether clear - but you kind of know you could listen to Byron spinning his tall tales all night.