Surface Detail is not the worst Culture novel that Iain Banks has written--that dubious honor is reserved for Excession, which meandered through an underwhelming tour of AI politics--but it's pretty close, and for many of the same reasons. I suspect it's a problem of scale: Banks writes fantastic micro-level scheming in both his science fiction and "literary" books, but he seems to lose the thread when he tries to translate that into galactic-level politics, especially for a civilization as ridiculously over-powered as the Culture. As a result, both Excession and this most recent book suffer from a chronic lack of action, and the characters aren't given enough urgency to make up the difference.
But at least this time it's better assembled, without Excession's random plotting and character introductions. Surface Detail's A-plot concerns an indentured slave named Lededje, who's killed by her owner during an escape attempt only to wake up again aboard a Culture ship light-years away. Understandably, Lededje wants revenge--something which, for obvious reasons, her rescuers frown upon. It's a nice way of introducing another shade of grey to the Culture's supposedly-benevolent interference in other civilizations: because Lededje's killer is powerful and wealthy within his society, the Culture won't help bring him to justice, because that would cause an unpredictable shakeup of the planetary order. At the very least they need a good excuse, even if they have to make one themselves--hence the scheming, courtesy of the famed Special Circumstances department.
Banks wraps Lededje's journey with a secondary, loosely-connected plotline regarding virtual Hells: the dark side of the Singularity's "nerd rapture," they're the result of mind-state digitization technology in the hands of religious zealots. Of course, not everyone is thrilled with the idea of VR programs dedicated to eternal torment. The pro- and anti-Hell sides decide to contest their fate by holding a virtual war (the Culture is anti-Hell, of course, but abstains from the conflict for some reason). So on one hand, the book follows a soldier named Vatueil, who's fighting (he thinks) for the anti-Hell side. On the other, it watches a journalist who became trapped in one of the Hells during an undercover investigation, and ends up exploring more of their nature than she expected.
These virtual segments give Banks a place to stretch out and indulge himself: his "war over Hell" takes place in simulated scenarios ranging from creatures living the core of a gas giant to Bolo-like sentient tanks. Likewise, his Hell is a nasty piece of gothic engineering, all torture and despair. Whenever he dips into virtuality, it's always a surprise. Unfortunately, it's also too vaguely described to get an idea of the stakes or what victory means in any given scenario, and it tends to kill the novel's momentum.
So that's the general idea of Surface Detail: 600+ pages of people struggling along in increasingly clever but implausible virtual environments, and Lededje slowly making her way back to her home planet for an all-too-short vengeance. It's a funny book in parts, an imaginative book in others, but not an eventful (or ultimately, satisfying) book. And in a setting as generous as the Culture, that's a tremendous shame.
Maybe it's impossible to do real societal intrigue and plotting in a Culture book. Previous books treated the highest levels of Special Circumstances almost as distant and meddlesome gods: the inscrutable missions assigned in Use of Weapons, devastating near-genocide in Look to Windward, and (most brilliantly) the manipulative, nested strategems in Player of Games. Attempting to give readers too much insight into the Minds running the Culture seems to either undercut the omniscience Banks grants them, or it leaves the main characters entirely powerless, or both. There needs to be a delicate balance between deus and machina--in Surface Detail, he unfortunately doesn't have the mix quite right.