I just finished Mary Doria Russell's novel The Sparrow. It's every bit as brilliant as I'd been told, but is a much different book than I'd heard. It's not a first-contact story (well, it sort of is, but only in the sense that this is part of the plot; look at the structure and a different theme takes precedence). It's a powerful portrait of the experience of spiritual betrayal.
It's also fairly brutal. I'm not sure I could recommend it for most people, in good conscience. But it is mightily well-written, and you'll never forget these characters once you have encountered them.
(Has anyone else read it? I feel the need to discuss, but do not want to put spoilers in the post itself. Comments are fair game.)