For the purposes of this review, I will assume the reader is already familiar with the Culture series of novels. If you have not read this series before: "Player of Games" and "Consider Phlebas" are both better introductions (and better reads).
This book has a very complex plot and a huge cast of characters. The Glossary and Cast of Characters alone are nearly 20 pages. To simplify greatly, the story follows three characters: the two sons and single daughter of King Hausk, lord of Sarl, a technologically backwards (approximately 19th century) land inside a "ShellWorld"...an ancient, artifical world of nested levels like Russian dolls, complete with nuclear suns and a variety of unique landscapes. The daughter (Djan) has long been away, adopted into the Culture and recruited into Special Circumstances. When their father is killed, one brother (Ferbin) flees their home looking for help from another SC agent who once helped their family, or failing that, his sister. The other brother (Oramen), unaware of his brother's fate or the great personal danger he is in, stays behind as prince Regent. Meanwhile Djan is travelling home upon hearing of her father's death.
Ferbin travels outward: literally out of the interior of the Shellworld, out into space; and figuratively outward from a cultural backwater into the enormous domain of the Culture. Meanwhile, Djan is following the opposite course, inwards from the expanses of the Culture to her old home. While Banks does an excellent job of developing the unique personalities and backgrounds of the 3 characters, they are primarily used to reflect on the universe he has created. Ferbin is the simple provincial, exposed to and struggling to understand the size and technological wonders of the Culture, while Djan is the sophisticated citizen of the galaxy through whose eyes we can see the Culture as it sees itself. The story of Oramen meanwhile allows Banks to describe their peculiar Shellworld home and contrast petty local politics with the grand scale of the greater universe. The book ends up almost reading as related travelogues. Having three characters in very different settings allows free rein to Banks's imagination as he conjures up world after world, alien race after alien race, technogical marvels, magnificient landscapes and colorful peoples.
The title of the book comes from one character's pessimistic philosophy: we must be living in a totally materialistic universe, because no created universe with a purpose could be so miserable and random. The central plot is around politics in Sarl, but the events, so grandly important and historic to the kings and princes of that land, are unnoticeably trivial on the galactic scale. Banks reinforces this by having the Sarl be patrons of a space-faring race called the Oct, but they in turn are backwards clients of the Nariscene who are further clients of the Morthanveld who are peer to the Culture. Even the God of the Sarl is merely a representative of one of the ancient galatic cultures, and not a particularly formidable one. For a science fiction book, Matter contains a lot of thinking about the meaning and purpose of life.
Unfortunately, after nearly 500 pages of exploring the Shellworld, the galaxy, a series of ancient mysteries and the psyches of its major characters, the book rushes to a unsatisfactory conclusion. I do not mean that there is no happy ending...this is Banks after all and the only thing predictable about the ending is that it is unpredictable. That is the great merit of the plot. Rather, the ending is highly anticlimactic. The book ends with a literal bang, but the buildup has gone on so long that tying it all up in 80 pages is far too brief and disappointing. After spending whole chapters on conversations in pubs and descriptions of making travel arrangements, Banks starts skipping over major events like battles and the deaths of major characters...dismissing them with asides and after-the-facts. This compression continues to the very end, where major events transpire in pages and finally paragraphs. This may be the final expression of the book's philosophy: the reduction of major characters and plot-lines to throw away sentences, but it feels more like Banks ran out of space or time. That a character in the last few pages is literally a God in a Machine may be clever, but does not excuse the Deus ex Machina feeling of the end.
I enjoyed the descriptions of the Culture, the Shellworld, etc. But it took too long, and the ending is unsatisfactory on many levels. "Matter" is well written...on a page by page basis ranking with Banks's best, but I can't ever imagine wanting to re-read it or recommend it to someone who isn't a Culture devotee...thus my 3 star rating.