Amazing in it's breadth, the story runs the gamut of laugh-out-loud funny to downright depressing, wisking you from London to the Highlands to the west coast of Africa and back again in a whirlwind. I couldn't put it down, reading through the whole five hours of a cross-country fight. But eventually the story stops being funny, stops being ironic, stops being insightful, and becomes unremarkable. I agree with others: Boyle should've ended this book a hundred pages earlier. It's as if he had the idea to run two stories and characters together, but got there faster than he thought, and then wasn't sure where to go.
But because the majority of the book is so good, and because by the time the story starts to go lame the key plot line is really finished, I still highly recommend it. Boyles command of language and vocabulary is especially noteworthy, and he raises some good questions about the nature of exploration, cultural perceptions and what we perceive as civilized - or uncivilized - societies...with a dose of sex, drugs and clarinet music thrown in for good measure.
(Note: written twenty years ago, it's also interesting to consider his depiction of Muslim peoples in light of the situation in the US, Middle East and Africa the last few years.)