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I used to be a huge fan of this series, but I think this is the book that made me quit reading it. Kenyon is big on tortured heroes (often literally tortured), and she went overboard in this book. Plus, after 14 books (or 13? 11? not sure) of anticipating who she might pair Acheron off with, I recall being extremely disappointed by his heroine, who was one of the more uninteresting ones in the series (or maybe I was just really over the series by then).
It's a huge book, though, and if you're interested in the series at all, I think you could easily skip to it after reading one or more of the earlier entries in the series. Just be aware that there is a LOT of on-page suffering.