I finished it. It's very good, and very weird. The aliens are even weirder at first glance. Probably the most genuinely alien species I've seen in sci-fi while still remaining comprehensible and somewhat believable.
They look like eight-limbed brittle stars, balls with scrungly limbs. They reproduce by budding off of a stack like jellyfish and have no DNA, instead they're shaped by just the physical interactions of their proteins and the magnetic field their "spaceship" generates, which itself seems to be alive and intelligent on some level completely alien to terrestrial biology. They have no brains, all their cognition is done in their sensory and motor neurons when they're not moving, which makes them ludicrously fast, an eye on the limb can see something, process it, make decisions about it, and send the appropriate reaction to the limb and execute it in the time it takes a signal to go from your brain to your elbow. At one point one of them turns itself invisible to the protagonist by mapping his neurology off the nerves' EM fields, reverse engineering how it all works, and noticing that his optic nerve doesn't transmit while his eyes are moving. So it staccato moves only when his eyes are moving and he can't see it even though it's right in front of him.
They also perceive human language as an attack. Since they're non-sentient they have no concept of selves or emotions, which makes 99% of human communication completely meaningless to them. So when they pick up human transmissions, they see this obviously artificial, highly complex and rules-driven signal that when translated contains no information. They interpret it as a virus, a trick to make them waste calories digesting nonsense signals. So in that initial conversation where they realize the aliens aren't sentient, the aliens I guess think they're engaged in some kind of energy-burning battle. There was never any chance of diplomacy, the war started before humans even realized there were aliens.
That all ties into the name, "Blindsight." That the executive function of the brain is superfluous to intelligence, it sits in the head and rubber stamps decisions made by other parts of the body, but when you reach out and touch a hot stove or something goes flying at your head the unconscious body works perfectly fine with no executive input. Works better even. Blindsight being the thing in cortical blindness where the eyes still work and the body can make decisions based on visual input but the executive isn't receiving any of that info. So the guy is blind but can still avoid obstacles as he walks, catch thrown objects, etc.
It also has an interesting thought on the Carl Sagan "spacefaring civilizations must be friendly or they would've destroyed themselves with the technologies required for space flight. Not a spoiler, it's discussed pretty early, the idea "technology implies belligerence." Technology, tool use, is a response to a hostile environment, a weapon for forcing the world into more amenable shapes. We build houses because we can't cohabitate with the world as it is. In the book mankind is starting to stagnate because we've reached the plateau where we're no longer under constant survival pressure, people are spending all their time chilling in VR collecting welfare checks while AIs and "bleeding-edgers," people loaded with extreme implants and genetic modifications to the point of barely functioning like humans, do all the work. The main character's a synthesist, someone who can collect, correlate, and summarize data without actually understanding it (the chinese room metaphor comes up a lot) because the bleeding-edgers are so far beyond baseline humanity that their discoveries border on incomprehensible. Again the consciousness metaphor there, baseline humanity as an increasingly superfluous rubber-stamping mechanism that doesn't contribute at all to the functioning of the body, just sucks up calories.
That's a tangent, but the point of the idea it's grappling with (not sure if I agree, it's not a polemic, just a hypothesis of what alien life might be like) is that Sagan's enlightened species would not feel the need to travel beyond the stars in the first place. Technology comes from a worldview that sees life as a war against reality, and only species that never lose that worldview will achieve interstellar flight because they're the only ones that will feel like they need to.
It's strongly implied that there are probably millions of Rorschachs out there scattered like dandelion seeds, that the aliens probably do nothing but build their giant living orbital habitats around brown dwarfs, then use those to make more seeds and spray them out. The vampire character is certain that the one that attacks in the book will not be the last.