Elizabeth is played by a guy?

A constellation of unrelated but very apt factors, I think. Firstly, I don't don't think of Quentin Crisp as a guy. He was very famous in Britain for being the campest well-known gay figure ever. I don't know if you know that the term "queen" is sometimes used to described the kind of bitchy, intelligent, sarcastic and profoundly imperious gay men that used to be found in the UK (I haven't met one for a teribly long time) usually deeply involved in the arts somehow, often as theatre directors or producers, keen on aftershave, wearing purple, expressing themselves and all things sensual. Quentin was the original poster child for this sterotype, the Queen of Queens. The Director is making a tongue-in-cheek sort of pun - "look audience, a queen is playing the Queen!" It's also very appropriate that the strongest example of the gay "queen" (in the culture of the UK) is playing the strongest example (in the culture of the UK) of a real queen of England - Queen Elizabeth I.

Also the whole story is about the blurring of genders and gender stereotypes. Queen Elizabeth was famously a rather strange blend of great feminine beauty but intensely (in the lingua franca of the time) masculine resolve as a leader in military affairs and other affairs of state. She never properly took a lover. Quentin Crisp was a very strange man who refused to hide his sexuality when he was a young gay man before WWII in London, very thin, and, like Elizabeth, had skin that was almost white. He also dyed his hair shocking red with henna. He painted his fingernails and wore lipstick long before there was any appreciable gay rights movement and walked about publicly in the streets, typically to taunts and jeers. He never allowed such treatment to change his behaviour. He was a very strong individual indeed. But also he had a certain regalness about him as this page from Wikipedia shows:

"As he had done in London, Crisp allowed his telephone number to be listed in the telephone directory and saw it as his duty to converse with anyone who called him. For the first twenty or so years of owning his own telephone he habitually answered calls with the phrase "Yes, Lord?" ("Just in case," he once said.) Later on he changed it to "Oh yes?" in a querulous tone of voice. His openness to strangers extended to accepting dinner invitation from almost anyone. While it was expected that the inviter would pay for dinner, Crisp did his best to "sing for his supper" by regaling his hosts with wonderful stories and yarns much as he did in his theatrical performances. Dinner with him was said to be one of the best shows in New York."

He was an astonishing and unforgettable figure, much like Elizabeth. He represented a very similar sort of hard feminity to the British public.

Another point is that the blurred of gender sterotypes is lent credence by his presence - a reminder that we already know examples of real people whose genders aren't expressed as we might expect.

So, I think it was a sort of tongue in cheek move to cast him as Elizabeth. A kind of pun.

I think it was very clever and wouldn't have worked at all if it had been anyone else.

I also think his performance was mesmerising...