This series depicts some of the most plausibly alien and unique cultures I've ever seen, an achievement which is in no way lessened by the fact that all of the cultures originate from Earth. Set in the distant future, the setting is remarkably rich and deep. The characters are diverse, and by "diverse" I mean 'these characters are all technically human and/or machine intelligences but their physical incarnations, thought patterns, modes of speech, etc. are wildly different'. Instead of different species and races, the setting has different neuroforms: base, Warlock, Invariant, Cerebelline, Mass-mind, etc. People are not defined by what they look like, but how they think. People can change neuroforms if they really want (and sometimes do), to the extent of people who were "born" as AIs incarnating as humans, and vice versa. Different neuroforms can be so incomprehensible to each other that they require translators, not for different langauges but for alien modes of communication and thought patterns.
The place really feels DIFFERENT: it's not "take modern Americans and give them some new tech toys and tweak a few cultural values". Even the characters who are have based their customs on Victorian England don't feel Victorian: they feel like a far future culture ripping off the parts of Victorian society they happen to like, using it for veneer, and ditching the rest. Like cosplay or the SCA taken to the next level.
The universe has history: mankind has gone through wars, technological breakthroughs and upheavals, obtained immortality, and continued to progress throughout. There is neither a sense of stasis, where technology remains roughly the same for long periods, and it's neither a unidirectional upward climb nor a post-apocalyptic waste.
IIRC, in the first book, Wright wisely avoided talking about lapsed time between eras. This one makes the mistake of talking about many millenia having elapsed and the main character himself being three thousand years old (and unremarkably old for the setting). I found those time frames unnecessarily long, but that's a minor quibble in a story which does such a great job of describing a society so technologically advanced it feels like an alien culture.
The story is rife with jargon based on English words -- neuroforms, the mentality, partials, dolls, Sophotechs, etc. It can get overwhelming, but the jargon does not feel obscuring or superfluous. Rather, it's integral: leaving it out would be like trying to write about 2014 without mentioning the Internet, smartphones, webpages, blogs, etc. It's jargon, but it's also part of everyday life.
The setting is easily the strongest point of the series. The characters are weaker by contrast; there are occasional points where I was thinking about the author puppeting the characters through dialogue, instead of feeling immersed in the interaction. The plot is reasonably engaging and kept me thinking. The main character spends a lot of time fending off accusations that he is insane, and the reader is left really wondering if he is, in fact, crazy and maybe even an unreliable narrator. ("Why don't you think you're crazy? I am pretty sure I'd think I was crazy in your position.") It's well-done, and the resolution of this point is wonderful.
There are some weird artifacts of 20th century thought: the narrator inexplicably refers to adult women as "girls" and there are conversations about gender-based roles that are at odds with a far future world where a number of (minor) characters have nonstandard genders and where biological sex is obsolete if not meaningless.
Even so, overall I found it one of the most wholly-realized futures I've seen depicted in sf. I wouldn't say "this is how I expect the future to look", but it feels real in a way sf rarely does to me. Real in that there is so much that is unrecognizable, so little that can be taken for granted. It's got flaws, but for that alone I have to recommend the series. The individual book I'll rate at an 8.IIRC, I like The Golden Age better, but both are well worth reading.