Existence

David Brin's Existence is both very interesting and somewhat irritating. The book has eight parts. The first six parts tell an engaging and interesting story which follows the adventures of several protagonists during a time of first contact. At that point I surmise that Brin decided that he just wouldn't be able to finish the book if he continued that way (at least not in a single volume). Anyway, he radically changed the style in parts seven and eight. In those two sections we no longer see the protagonists meeting challenges as events unfold. Instead, the story takes great leaps forward in time, pushing to story forward. Some foreshadowed adventures and events that I was anticipating were told only in hindsight. This let Brin finish the story in one (big) book, but at some cost to the storytelling.
Existence is chock full of interesting and provocative ideas about what the future may bring. Whether it is technical, scientific, social, economic, or you name it, the book touches on most everything related to, yes, existence. Brin's imagination is rather amazing. The book is worth reading just for that. And, the first contact idea in Existence doesn't fit any of the standard SF tropes that I know of. It is quite an unusual and interesting idea.
Conclusion: While Existence doesn't tell as good a story as some of Brin's earlier books (for example, Startide Rising and The Uplift War), it is still a good read, especially for those who like hard SF.