I wholeheartedly second your regret - although the plus side was that it helped me branch out and discover a bunch of new authors. While I'd do pretty much anything (ok, within reason) for more insights into Banks' mind concerning the Culture, I discovered there are also some other very good world/universe-builders out there.Interesting review Anthony. I'd held onto The Hydrogen Sonata until just a couple of months ago. I agree, while not the best Culture book overall, it is still one of the best sci-fi novels of this decade.
I find it difficult to make absolute comparisons of the individual Culture books as they layer so well into the Culture universe as a whole. For me the only way to look at these books is as a great history of this fascinating universe. I regret greatly that we will never see any deeper into this world.