If you're visiting London and enjoy musicals, I definitely recommend taking a trip to the Apollo Theatre to see "Wicked".
A retelling of "The Wizard of Oz" from the perspective of The Wicked Witch of the West, this musical has unexpected depth. Laden with left wing observations such as the human tendency to vilify (in this case, to literally have a "witch hunt"), how history can be manipulated to support the victors, and how life is about perspective.
Musicals aren't exactly known for complex characterisation, so it was an added bonus that the characters developed. They begin reasonably insipid and one dimensional, but as they experience injustice and pain, they grow and develop. The story is primarily about how the influence of one person can change you for the better.
But hey, it's not all Kant either - there's some good jokes, great set design, and cool lighting effects. The music is a little cheesy, but you're guaranteed to come out singing.