This is a very, very good book. Superbly written, plotted and paced. The sheer number of awesome science fiction ideas touched on in this book is mind boggling. Simmons could have written a dozen or more novels using the ideas in this one book.
The only thing that keeps Hyperion from a five star rating is the ending, there really isn't one. The book just sort of stops. I assume the story is finished in the next book. I suppose this is fine but it is something of a peeve of mine. I started the book under the impression that I would be reading a completed story. I understand that many authors write series of book where they continue an overarching story but in this case I felt cheated by the failure to complete it.
All of the above considered, I would still very highly recommend Hyperion. A very well done book and I am cautiously optimistic about the sequel, Fall of Hyperion.