"On the Mohs scale of sci-fi hardness, Blindsight is aggregated diamond nanorod." - AngryParsley
The aliens made First Contact via thousands of probes that photographed Earth down to a one-meter resolution. The human response was tiny, specialized, and fast-moving in pursuit. Everyone in the crew of five was something more than human, super-charged by genetics, surgery, and technology. Our protagonist is their Synthesist, a generalist who can explain the specialists to everyone back home; he explains the unusual well because he had to re-learn humans from the ground up after half his brain was removed.
...that distance—-that chronic sense of being an alien among your own kind—-it's not entirely a bad thing. It came in especially handy when the real aliens came calling.
The book has a collaboration rather than a tension between plot and ideas. Pondering philsophical, psychological, and scientific concepts is a part of understanding the action, not a distraction from it. It is a great sign for the writing when a discussion of human consciousness can be woven into the climax and add to it.
The book deals heavily with human brains and minds and the alteration thereof. No one in the main cast is an unaltered human; all have varying advantages and disadvantages from their alterations. The linguist is the most notable, constituting half the crew because she has surgically induced multiple personalities that work as a team; it is an upgrade, not a disorder. There is not discussion of what it means to be human so much as laying out some near- or transhuman minds and offering them for your inspection.
There is a progression in the book from humans to aliens to all minds. The beginning focuses on what has happened to humanity over the years, a conglomeration of technical advances that are mostly considered briefly. Humans can be refitted or upgraded, although many have retired and let the computers do all the work. Many uploaded permanently to their own virtual worlds.
The crew makes First Contact with the aliens, which gives us a chance for exploration. They are alien, not humans with rubber foreheads or in monster suits. I will not spoil it.
The interaction of the two lead to consideration of all minds. What does it mean to be human, particularly in a trans-human world? What does it mean to think, to be intelligent or conscious? And does it matter?
The book takes seriously the notion of the Cartesian theater. Do we see things directly, or is there some sort of little man in our heads viewing it all on a television? And then is there a little man in his head, and in his, and so on? The Cartesian theater sounds a lot like nonsense, but broken brains give us evidence that the brain might be processing things that way. The cast exhibits some of the evidence, and other cases are discussed. The titular "blindsight" is the case of receiving input that your conscious brain is not processing but might be available to subconscious or reflexive parts of your brain; your eyes and brain are still seeing but "you" are not.
Does there need to be any sort of "little man" or "I" at all? If you can have intelligence without consciousness, why have consciousness? A universe of computers that do not know they exist would be so much more efficient. (The book also takes seriously the notion of philosophical zombies. Yes, that is an actual academic term in theory of mind.)
Blindsight flirts with theories of consciousness early then backs away until they come to the fore of the plot. If you are reading gradually, you will have time for the information to sink in (or to be forgotten). I will leave it to the book, rather than carrying on. As I said, the philosophical lines grow with the plot, rather than infesting or displacing it, and you will enjoy their emergence.
I like the way that the speech is presented as having been translated. The characters speak in multiple languages, communicate with gestures and syllables, use computer assists, and are otherwise more efficient than baseline human conversation. Our narrator translates this into normal speech for us. The hidden fact of this succeeds better than Asimov's presentation of discussion within the Second Foundation or Scazi's under-use of digital telepathy. Surprisingly, it does not lead to mid-action info dumps, instead keeping things succinct.
The science fiction is very hard. There are 22 pages of notes and references explaining the science behind it. Kudos for putting that at the end rather than trying to shoehorn it into the plot. I saw nothing obviously wrong, although I am not qualified to comment on most of it, and it would take me a good deal of research just to pick out which parts are completely made up rather than based in a live theory.
The character development is foundational to the book. We spend most of our time with five characters, plus a few more in flashbacks. This gives plenty of time to develop them, some more than others. They interact with each other and display their differing views without necessarily sitting down for the info dump formal speech/debate. They are all likable in various ways. It is helpful to have a narrator who professionally sees what people mean, bringing our third person limited narrator slightly closer to an unreliable third person omniscient.
The book considers the borderline between created and "natural," machines and organisms. It considers the edges of consciousness and intelligence. It explicitly references Chinese Boxes and the question of non-intelligent parts in intelligent systems. In addressing intelligent systems, it does not then go on to conscious systems, where Gödel, Escher, Bach ponders whether a hive could be collectively conscious (the way our brain cells are). Pursuing that question may or may not make the ending more cheerful.
The book is often a downer, but there is great enjoyment to be had in the details and in the telling. I will leave you to them.
Google notes this book as the only instance in existence of the phrase "treacly invaginations."