One of the best hard SF books of the last decade and most original first-contact stories you're likely to encounter. You've never met aliens like these before. It many ways, it's a mediation on consciousness and different ways of perceiving reality, using a post-human crew on a first-contact mission as a way of delving into these issues. It can be a bit of a hard read, but it's more than worth it. And it's got one of the most original, biologically sound (scientifically) vampires you'll ever meet in fiction. I've read it twice now and it was even better the second time.