Having previously read "State of the Art", "Use of Weapons", and "Against a Dark Background", I've started filling in gaps and reading the rest of Iain M. Banks Science Fiction novels.
"Excession" is one of the best I've read so far (second only to the original "State of the Art" novella in my mind). I particularly like the details of the machine culture that sits parallel to (and in some ways governs) human society.
As with other Culture novels, "Excession" has a rich cast of characters and settings. The Affront culture in particular stands as a nice contrast to the tolerance of the Culture.
Banks has imagination to spare, and every aspect of the story just drips novelty and wit. Here's an example: as with every other experience in the Culture, childbirth is no longer an inflexible biological fact limited to one of two sexes. An individual in the Culture can change sex at will, get pregnant as a woman, and then become a man again, holding the fertilised egg in suspension indefinitely.
The story itself is more coherent than "Against a Dark Background", and ties together the various scenes better as a result.
This is a good book, one of the author's best, and well recommended.