For the most part of the book, I thought it's good though not great, 3 stars. Just thought I might give it 4 stars anyway, just because of the sheer number of ideas presented.
If a smorgasbord of ideas is what you like, you might enjoy this book a lot.() The author clearly put some thought into many of the topics discussed.
But that just makes the places where he didn't all the more jarring. There are many things that don't make any sense in context, or just aren't believable at all. Sometimes they're small, but they sill disrupt the narrative. So on one hand, you have the main parts of the narrative and the justifications for them explained in excruciating detail; on the other, a few paragraphs later you're presented with some clearly ridiculous notion you're just expected to accept at face value.
The plot mostly just serves as a way of stringing the various ideas together, so they can be presented (which I don't mind in principle); most characters are flat and undergo no development at all (ditto). And while I generally also don't mind characters waxing philosophical about one thing or another, here it sometimes seemed to devolve into hackneyed platitudes.
However, about the last quarter (or fifth?) of the book was pure nonsense. Just a ridiculous pile of drivel that completely ruined the book for me. That's why I'm giving it 2 stars in the end. Pity: first three fourths I enjoyed despite its shortcomings, only to be then unable to stop rolling my eyes and wishing it would end already.
() But then you might be better off reading one of Greg Egan's books, like Diaspora, or the Clockwork Rocket.