Descent

Great concept and execution but the best thing about this book is also the worst.

I loved how many different plot points came up throughout the huge adventures story, touching on science, religion, history and philosophy, but many of the questions raised are never actually answered. Normally I'm a stickler for tying up every plot point but it's a testament to the core plot (which does get resolved) that I actually didn't mind not finding out all the answers.