Okay, first things first. This is the first book I've ever read that might be considered "hard" science fiction, or the sort of sci-fi that tends towards technological speculation. I've just never been terribly attracted to that sort of book. Use of Weapons also has a pretty prominent military component, which has never been my thing either. So, the only reason I picked up Use of Weapons in the first place is because someone I really respect *loves* this book and I figured, it must be worth reading, even if it isn't the sort of thing I'm into and....
I loved it. Like, really loved it. As in, Use of Weapons, in all of it's hard sci-fi glory, is now in my list of top 10 favorite books. Seriously, it's awesome. Really.
Quick caveat. For reasons that I can't get into without totally wrecking it, there are people who find Use of Weapons to be "dark" or disturbing or genuinely upsetting. The book examines what might be considered uncomfortable territory from a moral point of view, and I can see why it strikes some readers as difficult. All I can say is that, for me, though affecting at times, I was too jazzed by what Banks was doing to be disturbed by it, "it" being something that I can't talk, so I'm going to stop referring to "it" and move on.
Very generally speaking, Use of Weapons is a sort of non-linear biography of Cheradinine Zakalwe, an operative for the Culture's Special Circumstances department. He makes, runs and strategizes wars and is a very bad man. He is also charming, fractured and funny - as is much of the book itself (discounting certain parts).
The biography is comprised of two separate narrative streams. One moves forward with the present operation, the other moves backward in Zakalwe's life, slowly revealing his past. The two streams alternate chapters and are book-ended by two very important prologues and an epilogue. This structure can be challenging at first, but once you find the rhythm, it becomes intuitive and fairly seamless. This structure was a bold choice on Banks' part - it asks a fair bit from the reader, but it works brilliantly as a reflection of Cheradidinine's psychological make-up.
And that's really at the heart of the book - Zakalwe's social and psychological make-up (which is probably why I enjoyed the book so much). Use of Weapons is a sort of onion-skin portrait of this character. As more and more gets revealed, the reader's understanding grows until the climax blows general expectation out of the water. Fantastic.
Though I can see why this isn't widely considered Banks' best book - it straddles literary fiction and genre with its structure and subject matter - it's a brilliant book and I wish it were more widely read. Regardless of where you categorize it, Use of Weapons is truly speculative, not just technologically, but socially and psychologically as well. I loved it. Even if I had found the "disturbing" portions difficult, I think I would have still found that the book as a whole very much worth the disturbance.