When I was on page 305 of 'Matter' I wrote myself a note:-
"So far so nearly good. Apart from a gory murder early on this Culture story (which isn't totally a Culture story as it's set on a world beyond the periphery of the Culture) is almost entertaining enough, actually funny in places. The shell-worlds are an interesting and convoluted idea which could only have come from Iain M Banks' fervent imagination. There's just a little too much description and back story/side story/technical and/or political and/or philosophical detail which holds up the narrative."
Now I've finished its almost 600 pages I still agree with my previous thoughts but I have enjoyed the novel, despite the convolutions which are mainly in the technological descriptions not the narrative. There is much humour, especially in the heightened dialogue and philosophical discussions between human and alien characters. Despite plenty of murder, gore and mayhem, 'Matter' is not as dark as, for example, Ian M Banks' earlier Culture novel, 'Use of Weapons'.
The three main characters are: Ferbin, Prince of the Sarl who does not want to be king, Holse, the Prince's right hand man and probably the most intelligent human present, and Djan-Siery who is Ferbin's sister and not what she seems, having spent time visiting the Culture and being adopted by the Culture's Special Ops department.
With part Medieval cultural beliefs and steam-punk technology, the Sarl become embroiled in an unexpected conflict which nearly leads to the destruction of their home land and the entire colossal shell-world on which they occupy the eighth level. Only Ferbin, Holse and Djan-Siery can save the world...