I just read four books in a row by this one author: Newton's Cannon, A Calculus of Angels, Empire of Unreason, and The Shadows of God. I had to.
I got lured into this steampunkish, alchemical early 18th century tale featuring Benjamin Franklin, Isaac Newton, Louis the 14th, and many of their historical friends and enemies -- and as you can guess from the front end of this sentence -- the first two books were riveting and amazing and demanded I read more -- and the final two were not nearly so enthralling for me.
There was so much that was wonderful about these stories: plot-twisty and fascinating, fantastical logic and inventions, with beautiful writing besides, and I think that is part of what drives my disappointment, because I really hungered for more of that in the last books. But in the last two books, there were many, many battles, and I'm not a reader of war stories. (How many times can someone's head pop, anyway?)
So, I don't know for sure that there was anything wrong with the writing or the plot twists toward the end, or if the premise and style had started to wear thin on me after four books, but I can say very clever and interesting characters ended up (a) saving the world, (b) in a gigantic battle of immense proportions, and (c) everyone rushed into an ending where they lived pretty happily ever after in yet another stock-fantasy ending regardless of their personalities, with (d) no real deepening or growth of their characters, except marginally, for my favorite, Adrienne. Adrienne was consistently great.
Again, important writing lessons. There is a price for all action, one paid before, and one paid after. You might, might be aware of the first price, or at some point become aware of what you have paid for the privilege of making your own mistakes. But there is no way you can prepare yourself for the second, the price you pay for what you have done. I think this is what most endings -- including my own -- are missing.
That second price... that second price...
And Mr. Keyes has written other books, which are probably equally clever...