The Lost Symbol - Dan Brown

Vivian and I just finished reading Dan Brown's latest Robert Langdon thriller, the Lost Symbol.
I did not enjoy it as much as the DaVinci Code, or even his earlier Angels and Demons.
For the first 4/5th or so of the book it was the expected "pot boiler," but after the character Mal'akh dies, it became ONLY an investigation on the spirituality of human nature.
Of course, we are very interested in the spirituality and philosophical aspects of Brown's writing and we continued to be spell-bound as he unravels the hidden nature of the universe.
However, as a literary work, I feel that the book was not well-crafted. In a well-crafted novel, I would expect ALL elements of the story to continue in full suspense up to the denuement, and then come quickly to the end.
Nevertheless, because we are interested in the spiritual or philosophic aspects of the books we read, we were not disappointed. But we feel that readers who want only the physical adventure may be.
Doug