I have just reread this novel, having been very struck by it some years ago. Perhaps it loses just a little of its impact second time round, because you are prepared for some of the shifts in plot and character, but it is still very subtle and absorbing, and the narrating voice is fascinating. It was interesting to read in the introduction (to the Oxford Words Classics edition) about the split between readers who are pro or anti the narrator Dowell. At different points in the novel Dowell seemed, to me, humane and insightful, confused and naive, cold, even cruel. He is sometimes described as an `unreliable' narrator, but he seemed more mysterious and inconsistent than unreliable, precisely. For me that was one of the most striking aspects of the novel - the effect is to make one feel unsure how to respond to *any* of the four (five including Nancy) characters, including the narrator.
It is very similar, as others have noted, to some of James's novels - particularly the late novels which usually focus on the (often morally dubious) relationships between three or four characters. Ford is rather less supersubtle than James (not a bad thing!) in that it doesn't take ten minutes to work out what a single sentence means and it is usually (more or less) clear, at least eventually, what the characters have actually done - even if questions still remain over how we should respond to their actions. So - a very rewarding and interesting novel overall.