The Book of Mormon
The Book of Mormon is a musical brought to us not only by the creators of South Park but also Robert Lopez of Avenue Q. Given this lineage, the humour in The Book of Mormon is both deliberately offensive and tremendously funny.
One thing tactic often used in episodes of South Park is to intersperse sentimental bits to break up the comedy, which makes the jokes seem funnier when they reappear, similar to how comedy can be used to heighten tension in thrillers and action films. This technique is used in The Book of Mormon, but for the most part the jokes are pretty relentless.
At its centre, the show is about the ridiculous things people believe, and why people believe them. We have the Mormon missionaries who believe that God lives on a planet called Kolob and "Jesus has his own planet as well." We have the Africans (most of the musical takes place in Uganda) who believe that raping babies will cure AIDS. We also have the audience who believe in alternating versions of Africa as home of The Lion King or a land of disease and death next to which the "Spooky Mormon Hell" pales in comparison. When you juxtapose all these beliefs, the show pretty much writes itself. It won't change anyone's mind, but it will make them laugh.
The music is competent but fairly forgettable. My favourite was the send up of Hakuna Matata, which becomes Hasa Diga Eebowai, or "Fuck You, God". It's offensive, yes, but it's not that offensive, is it?
The Book of Mormon is at the Prince of Wales Theatre, for years probably.