Actually the book wasn't that bad, there were parts that I really enjoyed.
Unfortunately there were lots of parts that had a "forced" quality to them. Trying to advance the Forgotten Relms into the 4E timeline (horrible mistake IMO) made the story into something less than what it could have or should have been.
I compare the book to the Lost finale just because for the first 90% of it it was entertaining, and while not up to the usual standards I have become accustomed to it was still worthwhile. The very ending of both the Ghost King and Lost made me wonder if the writers lost a bet or took some really bad drugs.