Storyline: 4/5 
 Characters: 3/5 
 Writing Style: 3/5 
 World: 5/5 
 In this satisfying ending to a very good series, Simmons entertainingly brings the story to a close. His world-building is at its best - both T'ien Shan and Startree now rank among my favorite fantastical science fiction worlds - and the storyline itself obviously received detailed inspection so as to plug, remedy, or otherwise respond to those nagging loose ends and plotholes. To straighten out the story, however, Simmons has to employ significant and repeated retroactive continuity changes (view spoiler)[ It turns out that Father Dure's musings from book one are wrong, and they are not necessary for anything in the following three books. Meina Gladstone was also wrong in what she thought about the TechnoCore and where it was located. So scratch that off the list of helpful information provided in book two. That ever-so-important scene with Ummon in book two (where we finally made sense of the identity of the TechnoCore and the different alliances, allegiances, and motivations) was also incorrect. That loss was particularly upsetting to me as it was a major source of organization and clarity for the first, second, and third books. Finally, and most importantly, we are told that Martin Silenus's Cantos (essentially book 1) are mistaken in untold and unknown ways. Essentially this means that whatever you thought you knew from the first three books is suspect and anything written in the fourth has priority. (hide spoiler)] The characters also continue to be a weak point in the series and Raul never does adequately morph into the everyday-man-turned-hero that Simmons wants him to be. Still, these minor distractions are insignificant compared to the great story, fantastic worlds, and thought-provoking science fiction contained herein. With this book in place, the series is now both remarkable and memorable. 
 Because it is so long and complex, it really is a book that is best read in a discussion group or with friends. Lacking that discussion group, I post some further thoughts, ideas, questions, and criticisms here. Everything hereafter should be considered as spoiler. 
 (view spoiler)[ 
 Taming versus evolving: I absolutely loved the idea, finally developed, of the contest between those who wanted to master and control environments for human habitation (terraforming) versus those who chose to evolve humanity to inhabit those environments (gene nanotechnology). The book convincingly conveyed the bigotry and fear of losing one's humanity (the Pax) and the utter liberation and possibilities once one relinquished that fear (the Ousters). I wish Simmons had pursued this a little more, because in this contest between visions of humanity's future, it was not possible for the two sides to reconcile. Simmons's characterization of the Pax, unfortunately, was of a faction that was utterly and thoroughly corrupt, and Simmons doesn't permit an honest voice of the conservative vision. He does provide the moderate, compromising characters for religion (the Dali Lama, and de Soya) and political system (Isozaki - whom, I will add, I was disappointed to see so little of), but in all of these cases they agree to join the progressive, evolutionary side of the contest. I found on several themes that Simmons's ideas were bigger and deeper than he even realized (or conveyed). 
 Human versus AI: The whole point of AI is that machines develop capacities beyond that which was conceivable. That is why it is interesting. But Aenea tells us over and over again that the TechnoCore will always be parasites - that is their nature and they can do nothing about it. I wasn't convinced with her (i.e. Simmons's) explanation, and I thought it unnecessarily limiting (particularly since part of the TechnoCore had created the Keats cybrids - doesn't that tell us that they can evolve?). In book two one of the main plotlines is the human versus AI battle. Simmons resolves it I suppose, but I lost interest once he had to rewrite so much of the story. Were I depending on that being developed fully and finally, I would have found this ending less satisfactory. 
 Time travel: Time travel was a big part of the first book, and I found it difficult to visualize and appreciate the significance of someone or something moving backward through time (I have problems with time travel stories generally, so maybe its just me). After book one the whole time travel element becomes a small descriptive element and isn't a part of the main storyline anymore. Of course, we get Kassad and Rachel, but I didn't understand what role they were playing in the book at that time, how they got there, or where they were going to go after that. Specifically, I didn't see how what happened with Kassad and Rachel in book 4 mattered to the events that happened in book 1. Simmons did the same thing with Het Masteen's treeship. It was renamed the Tree of Thorns... That suggests that it somehow is going to be the Tree of Thorns that appears at the end of Book 2, but in book 4 it also suggests that the treeship goes back in time to the events of Book 1 and is destroyed there (as it was described in Book 1). Finally, I found it bizarre that whenever someone traveled through time (Het Masteen and Aenea in particular) that the time they spent in the future was the same time that was lost in the past. If Aenea spent twenty-three months, one week, and six hours in the future, why can't she be returned to the past at the same moment she left it? Why does she have to disappear in the present for the same amount of time? This is where a discussion group would have been particularly helpful - I suspect that in the preceding 2,272 pages I missed something or was working from a false assumption or misunderstanding. I'm fairly certain, though, that this is not the way in which time travel is generally portrayed. 
 Martin Silenus: His character was awful. I know he was crude and arrogant in book one, but you don't need to remind me with every single sentence. He also had some sensitivity about him which was entirely lacking in this book. Also, I see why Simmons thought it would be nifty if Silenus had actually been touching the Void Which Binds for the last couple hundred years, but it creates two other problems: 1) a large part of the Cantos had been written long before that, so his belated access to the voices of the dead wouldn't have helped him for those portions. 2) If he had the sort of future- and past-knowledge that Aenea did through the Void, why did he make so many mistakes in the Cantos? 
 "This is not metaphysics, my dear friends.": That is exactly what it was. You are presented with a charismatic figure that claims to hold knowledge that cannot be learned or verified in any way unless you trust them, accept nanobots into your bloodstream, and then follow the teachings of the charismatic leader as to understand what happens to you. Are you crazy?! You just filled your body full of machinery which you have no idea how works or what it does. The only reason you have to do so is because you trust a person who says they can hear voices and commune with the dead. This is a by-the-books example of a religious cult. And it was just downright bizarre how Aenea didn't like for her followers to be called disciples, how she didn't like for the wine-drinking ceremony to be called communion, and how she had to sacrifice herself naked, under torture, and vertically affixed to a cross-like post. Everything here had the trimmings of religiosity - and none of it had to. No one studied the nanobots in Aenea's blood. If she were teaching science, then why didn't she? Why would you make the conversion ceremony a ceremony at all? Why put it in wine and drink it when they could have just delivered Aenea's blood with injections (you know, like real medicine, technology, and science would have done). And really, she has to go through a Christ-like crucifixion in order to have the Shared Moment? This leads to another point that nagged me throughout - love. Why is the Void Which Binds dependent upon love and empathy? Why not hate? If you want it to be a strong emotion and something which gives people a unique relationship - make it hate. I thought the attempts to make love some sort of Newtonian law were as ridiculous as to make Aenea's cult a science. Oh, and one final thought on this: I know "Choose again" was supposed to be witty and pithy, but it sounded like a philosophy an immature adolescent might adopt upon first starting to think for him or herself. 
 Raul's big fight: Really...? Raul is going to fight Nemes.... And he's going to hold his own in the fight... And he's going to make the fight last more than three seconds... I've always found Simmons's action scenes adequate - neither remarkable or distracting, just good fun and adventure. This was undoubtedly the dumbest, most indulgent, and worst action scene of the book. 
 Pedophiles: I'm not sure what it is about writing that seems to give middle-aged and older males the license to write out their sexual perversions and fantasies - and certainly Simmons is not the first to do this (I think this has been going on since men were writing) - but really? Do you have to push the boundaries on the age of consent? Simmons did this before in Hyperion, and I thought it was sleazy then too. 
 I'm probably wrong on some of the stuff in here. Sometime, I'll read through others reviews and look through discussion boards to see if these points have been raised elsewhere. Despite most of the above comments being negative, this was a great book. (hide spoiler)]