The Left Hand of Darkness.
Some spoilers below.
At first, I couldn't relate to this book, or any characters in it. But gradually, they began to grow on me. Soon, it was really a book about characters, and not so much about events. The events are incredibly bizarre, and I found myself grinding my teeth in frustration at the unrealistic actions and reactions the characters were having to events. Like, you spend a year traveling to a distant planet, and when you get there, you don't bother to attempt radio communication with the inhabitants, who you know have radio communication. You just put down and land. But, I understood -- if the characters acted with any common sense, the peculiar story would not have been able to happen, and the point of the story is to question our relationship with God and the universe, I guess.
So, in short, this is, without a doubt, the best book I've ever read about a priest getting sodomized by aliens.