I like Iain Banks and his Culture series very much, but Matter was a let-down for me. It’s an okay book, and that’s really quite disappointing copared to the potential of both the series and its own contents.
Matter shows us a lot of things I’m really interested in: We get to see somebody who is still in training to be a Special Circumstances agent, and she comes from a fairly archaic non-Culture world, to boot! This gives us a nice comment on the Culture from her eyes, and at least a bit of character development. This was definitely the good part.
But we get many more POV characters, and most of them weren’t all that interesting. Her two brothers, princes in said archaic world, drag the plot instead of carrying it (although those two definitely get most of the character development).
On the scifi side of things, again, we are introduced to many really cool things: Several different non-humanoid alien species with very alien needs and views and communication tactics. Different kinds of world, like the Nestworld and the Shellworlds. These are the things Banks is really, really good at. But sadly we spend about 10% of the book exploring these concepts, 80% with set-up maneuvering getting all characters to the point of readiness, and then 10% of an action-packed, sudden climax and resolution. With an appropriate amount of Meta, one character notes towards the end that war is “a lot of waiting and then a few short moments of uninhibited terror”. That’s Matter.