This is a typical Culture novel, if that phrase even makes any sense — a 500-page brick of a hardback release dense with the meaty, unapologetic heavy iron space opera that Banks does so very well. This stuff tickles my brain hard and makes me very happy to read, lengthy infodumps and long asides and all.
Like many of Banks' books, the central plot is interwoven with dozens of side plots, tangential events, and sometimes things that seem sheerly and gloriously random. This is not tight prose, and it is not casual reading. What it is, is smart as hell and a great deal of fun. Even if you've never read a Culture book before, it will make sense. It will make more sense if you have, of course.
After I finished The Hydrogen Sonata last night, I spent some time thinking about what the book did and what it meant. One of the basic critical questions about any story is "whose story is this"? Ie, "who changes or is changed most by events". In an odd way, The Hydrogen Sonata fails this test. Or more to the point, declines to be measured by this test in the first place. I mean, we have 500 pages of culture clash, space battles, the disappearance of an entire species, the machinations of the galaxy's oldest person, love, sex, betrayal, and of course, the Hydrogen Sonata itself. Yet at the end, with one or two exceptions, every major character more or less winds up where you might have expected them to from the beginning. (Except for those who got killed along the way.) Even Vyr Cossont, the nominal protagonist, seems to have the gentlest of epiphanies, albeit her journey to that point is very challenging.
And I think this is the point of The Hydrogen Sonata, inasmuch as it has one: the journey is the tale, not the destination. It's a heck of a journey, and I loved it. Delightfully dense, thoughtful, intellectually challenging stuff that's also a heck of a ride.