So, this was a tough one to rate. On the one hand, it's hard sci-fi through and through: heavily science-based and intricate, with time hopping and reality hopping galore, tech beyond all tech, and a vision of future humanity that involves so much gene manipulation and cybernetic enhancement that humanity as we know it doesn't even exist anymore. Add to that, some pretty complex visions of alien lifeforms and culture--most of whom are extinct during the time period the book spans--and you have an incredibly complicated, incredibly detailed backdrop for the goings-on of the story.
If you're into hardcore sciency sci-fi, you're in for a treat.
Unfortunately, I felt lost at times in the science and wanting more plot and character development. There are several key people playing major roles in this book, but they all felt a bit flat, in my opinion. They did things and had motivations for doing said things, but I never really connected with anyone. They all just were sort of there. And doing things. Because things needed to be done to make the larger story arc happen.
The plot itself is multi-faceted and twisting with revelations--YOU SEE WHAT I DID THERE?!--galore. And yet, there were places where hugely important and interesting events were skipped over and just summarized after the fact--like the whole Spindrift event. I found myself wanting to 'see' these, not just be told about them in a few paragraphs. I also wanted more of Captain Brannigan--to me, the most interesting sub-plot and character of the book--and who and what he was prior to this book. How he came to be what his. If there isn't already a book on this, there should be. I'd read the hell out of it.
I liked this take on AI, with limited machine AI in favor of large-scale investment in human physiology manipulation. Human brain AI, if there's such a thing, and data recordings--human reproductions of mental capacity, experience, personality. Basically, build a better human instead of a better machine, though that does tend to blur on the lines on what is truly human...
Oh, and the twelve-year-old in me kept giggling at references to 'Stoner society' and 'reefersleep'. Made me think of Cheech and Chong meets Bill and Ted or something.
So, do I recommend it? Yes. But only if you like a heavy, sciency read that's light-ish on action. This is not an easy read (at least, it wasn't for me) and therefore not for the faint of heart but it's well researched, well thought out and impeccably executed. Also well-written. I gave it three stars more because of personal taste--I would have liked more character development and action, and some leaning down of events and chapters that didn't really move the main plot forward--than because there is anything fundamentally wrong about the book or it's writing. So, if you like a heavy science read, perish the 4 and 5 star reviews--they won't lead you wrong.