The Hells are causing most problems because some civilisations (including the Culture, of course) think they are horrible, terrible places that should be abolished immediately. Others don't see the harm and don't like to have self-righteous interference in their running of their own affairs. As such, there is a war going on between the pro-Hell and the anti-Hell contingents. The war is being conducted in virtual worlds, at least at first.
Two lovers, sort of anthropologists, have agreed to visit one of the Hells so that they can report back how, er, hellish it is. They've been given one cleverly disguised piece of code each that will allow them to escape but only one of them makes it back to the "Real," while Hell's demons try to ramp up the torture of the remaining lover, attempting to raise and then dash hopes over a prolonged period (more than a lifetime of Hell years). To put it mildly, those who enter are strongly advised to abandon all hope on entering as it makes them harder to punish. The anthropologist becomes like the pilgrim in Dante and has to descend deeper and deeper to truly know Hell so that when she emerges, she reaches true enlightenment.
The description of this Hell made me wince a lot more than 127 Hours, although the punishment in the latter was very Dantean (or Aquinan)--for Aron Ralston, the perfect contrapasso for his self-centred life is putting him in a situation where he can't get out alive without the help of others. L'enfer, c'est les autres. Meanwhile, another Surface Detail character has experienced quite a different hell at the hands of others in real life. She is the slave of the richest man of her civilisation and, like all indentured servants, has skin (and teeth and organs) that are patterned with a beautiful tattoo. Her master has raped her repeatedly and after he goes one step too far, she is seeking revenge.
I often find Iain M. Banks novels tricky to get into, mainly because the names of the characters are so complicated and do encode the gender or race of the character. Surface Detail was particularly tricky what with the virtual worlds and reincarnations; like in Inception, you often have to ask exactly whose subconscious/Hell you are in (and whether an individual's death is actually a final death or just a temporary obstacle to overcome). I was gripped even by the first fifty pages, though, and persevered on. Unusually for me, I'm writing this post two thirds of the way through the book. This is partly because I think it might result in philosophy/theology overload and partly because I'm worried that by the end, I might have overthought it all so much that I understand it less. Good stuff, though.