I finished this one a couple of weeks ago, and have been half-assedly trying to concoct a coherent review of it ever since. This is more difficult than you might think (certainly more difficult than I thought it would be) because, on reflection, there's really almost no plot to the book.
And yet, I really, really like this book. It's certainly the best science fiction book I've read in quite some time (though that's not saying that much, given that the vast majority of my recent reading has been mystery novels written well before I was born...), and I would happily vote for it for any awards it might be eleigible for, were I the sort of person who voted for awards.
But damn, this is a hard book to describe.
Put it this way: This book was good enough to make me want to read Consider Phlebas again. Well, almost.
Taken as a whole, the book is basically an extended meditation on death and loss. It opens with one of the major characters dying pinned beneath a disabled tank, and really doesn't get any cheerier. The main story line concerns the events on a Culture Orbital which is about to be illuminated by the light of two stars which were destroyed in one of the closing battles of the Idiran War (the connection to Consider Phlebas. I'm not sure if this is a conscious parallel to Brightness Falls from the Air or not). The plot follows the events on the Orbital before, during, and after the arrival of the "light of ancient mistakes," mostly concerning the arrival of a Chelgrian emissary, a member of a species whose first contact with the Culture had disasterous results. His nominal mission is to try to convince Mahrai Ziller, a famous Chelgrian composer living in self-imposed exile, to return to his home world, but it seems clear from the start that his visit has another purpose. There are four major viewpoints/ plot threads, which weave around each other and eventually converge (more or less) for the grand finale.
The plot, were I to choose to spoil it, could be summarized in a fairly short paragraph. It unfolds at a rather leisurely pace, which is not at all the sort of thing I expect from an Iain Banks novel-- this is far and away the least frenetic of his books. And yet, it's never a dull read. Most of the book consists of blatant infordumps, but Banks handles them with an impressively light touch-- copious information about the Culture is provided to the reader through the simple device of having the main characters be outsiders, but it's woven into long stretches of snappy Banksian dialogue (the two-page conversation consisting entirely of cool Culture ship names is priceless), or set against the impressive backdrops available on the Orbital.
Which is not to say that the plot is buried in the infodumps, either. This is no Bruce Sterling novel-- if anything, the slow pace of events only serves to build suspense as the story unfolds (in a characteristically non-linear fashion). The pain and loss felt by Quilan, the Chelgrian emissary, is never far in the background, and tints the other sections of the book as well, servng as a constant reminder of what's going to happen eventualy.
This book ought to be required reading for a mandatory "how to introduce your far-future world" class for would-be authors. Look to Windward provides more information about life in the Culture than all the other Culture novels combined, but he never stops things dead, and every section has something to hold the interest of those who couldn't care less about the internal politics of the Culture.
There are a few flaws, most notably one entire plot thread which is only weakly connected to the rest of the book, and really doesn't go anywhere (it does feature a very cool setting, but it probably would've been better as part of a different story). There are also some problems with the Prologue and Epilogue-- the former sets up a bait-and-switch which some readers may find annoying, and the latter is too similar to the Epilogues of some of the other Culture novels.
All in all, I think this is the best Banks book I've read. The characters are easier to identify with than most of his earlier protagonists, but flawed enough to be interesting. The relative simplicity of the plot works in the book's favor, as well. It doesn't have the shock value of a Use of Weapons or The Wasp Factory, but the characters are better drawn, and the pervasive melancholy of the story is, if anything, more lasting that the gross-out value of his rawer earlier books. The overall effect is sort of as if Banks set out to write a Gene Wolfe novel, with a little bit of Larry Niven thrown in, and the whole thing turns out to work a lot better than that description sounds.
This isn't a book for those who demand whiz-bang action, and I'm not sure whether it would play well with the political crowd-- there's a lot of political content, but it's a muddled, compromise-ridden, real-world sort of politics, not the stuff of ideologues. But this is an example of one of the best writers in the genre working at the top of his game-- if you like SF with both good characters and cool ideas, it's well worth a read.