There's a quotation in the front of Sawyer's 1999 book Flashforward by Spider Robinson, stating that Sawyer is on his "(extremely short) buy-on-sight list, and belongs on yours". After reading Illegal Alien and the Quintaglio Ascension Trilogy, Sawyer was also on my buy-on-sight list, which is why I bought this book, and several others written by Sawyer, on a recent book-buying spree.
I suspect that Spider Robinson was as disappointed by this ensuing book as I was. Sawyer is no longer on my buy-on-sight list. You'll have to check with M. Robinson to see whether he is no longer on xyrs, too.
The disappointment stems from approaching this book expecting there to be a story told somewhere within it. Sawyer likes to philosophize. Both Illegal Alien and the Quintaglio Ascension Trilogy addressed major philosophical issues, but managed to do so by placing them within the framework of an actual science fiction story. However, Caulculating God barely does. There's scarcely any plot and zero characterization. It perhaps transmits the nature of the book best to observe that a good three-quarters of the prose has the protagonist working in his office, eating or interacting with his family at home, or lying awake in bed. The book is written in the first person, from the point of view of the protagonist. We hear about his ailments and thoughts at length. Apart from that, however, every single other character in the book is entirely one-dimensional and flimsy.
This book is not a work of fiction. It is a philosophical tract masquerading as a work of fiction. Approach it as you would approach The Screwtape Letters or some other such work, and you'll probably fare better than those who expected a science fiction book to contain an actual science fiction story somewhere. Pretty much the entirety of the book comprises the protagonist gradually arguing himself into being a Deist, covering some of the ground covered by 20th century thinking on the subject. Most of the prose is the protagonist debating various facets of the issue, and various stages of the argument, either internally with himself (one of the duller means of exposition of an argument in fiction — Asimov always ensured that Janov Pelorat was there as Golan Trevize's external foil for any arguments, notice.) or externally with either his wife or a visiting alien.
And that's pretty much it. Yes, there's the obligatory pair of U.S. fundamentalist Christians who, for unfathomable (or, at the very least, poorly explained in the book) reasons, decide to take a machine gun to some fossils. Yes, there's the dénoument, which in stark contrast to the slow exposition of the rest of the book zips by at breakneck speed (four months passing in one sentence, at one point). But those are completely overshadowed by the lengthy, tedious, seemingly endless, philosphizing.
When it comes to philosophical proselytization masquerading as fiction, C.S. Lewis is not in any danger of being usurped by Sawyer. The quality of Sawyer's arguments is not anywhere near on a par with that of Lewis'. Almost all of the arguments are a mis-mash of other people's writing and thinking, from Arthur C. Clarke through Larry Niven to Richard Dawkins, peppered with enough name dropping that it makes the reader want to sneeze. The result of stirring so many things together is a bland and thin soup of an argument, with fallacies in it that anyone with a basic knowledge of statistics and probability theory (in particular, how one derives probabilities, to determine whether something is actually improbable in the first place) can spot from a mile away.
As a work of philosophy thinly disguised as fiction, Calculating God fails. But as a work of science fiction, it also fails. The alien is far from believable, and there are several massive inconsistencies.
Sawyer may drop Larry Niven's name from time to time, in this book and others, but he clearly hasn't paid attention to Niven's actual writing. Sawyer's main alien, Hollus, has an excellent grasp of the spoken English language that isn't disturbed by either stress or the lack of use for several years. A minor plot point in at least one of Niven's works is that the Puppeteers forget the correct inflection and intonation of human language, resulting in their speech becoming flat and toneless, whenever they are highly stressed. Anyone with a second language will know that it is more difficult to command that language fluently in times of stress. And even presupposing that the alien's brain is wired such that it doesn't suffer from this language problem in the way that human brains do, the book actually states outright at least one linguistic failure mode that the alien's bipartite brain is prone to. Yet this doesn't actually occur. It seems that Hollus is not intended to be a believable alien, merely a convenient foil for the protagonist's philosophical arguments. Thus adequate grasp of English, even during crises, is necessary for the character, even though it is inconsistent with the conception of the alien and with the … cough … story (such as it is). The one attempt to make it appear, all other appearances to the contrary, that English is not the alien's first language, the inability to pluralize Greek and Latin words (leading to it saying things such as "phenomenons"), is a highly transparent sop, made even more so by the alien's excellent grasp of Greek and Latin accidence whenever the conversation turns to the names of constellations. He cannot pluralize "phenomenon", but has no trouble, it seems, working out the genitive of "Draco".
Similarly, the aliens' technology and civilization, what little is explained of it, is highly inconsistent. Supposedly, the aliens know little more than the current human race does; and one of the bases for the entire argument is that they are at relatively the same stage of cultural and technological evolution as humanity, merely having discovered one more fundamental force than humanity has. (In fact, humanity thought that it had discovered a fifth force in the 1980s. For more on this, read The Rise and Fall of the Fifth Force: Discovery, Pursuit, and Justification in Modern Physics, Allan Franklin and Clinton Van Siclen, American Journal of Physics, June 1994, 62(6), pp. 574–575, doi:10.1119/1.17526; Ten Years of the Fifth Force, Ephraim Fischbach and Carrick Talmadge, arXiv:hep-ph/9606249; and then this article in Astronomy Today.) Yet these aliens are capable of holographic projection into thin air, the creation of immaterial force fields, immaterial remote sensing equipment, and continual monitoring of the entire celestial sphere from a single spaceship in geosynchronous orbit that is better than the entire human race is capable of using its entire arsenal of ground-based and orbiting telescopes. None of these are within the grasp of current human technology.
Again, the aliens' technology is transparently a device to allow the alien characters to be both the instigators of and the foils for the philosophical argument that is the book's clear raison d'être. That an admittedly violent race hadn't adapted force fields into personal force shields, which would have prevented one of the aliens getting hurt, is one of the several inconsistencies in the aliens' technology. Again, paraphrasing Niven (from the afterword of The Long ARM of Gil Hamilton), internal consistency is one principal measure of an SF story.
Science fiction fans will be disappointed by the lack of hard science, the inconsistency, the poorly imagined aliens, and indeed the lack of much in the way of a real story (fulfilling the "fiction" part of "science fiction"). Philosophers will be disappointed by the poor expositions of the various arguments, and the crass admixture thereto of random pop culture referents such as Eric Cartman from South Park. Statisticians will want to point out the gross and wholly unsupported assumptions about probabilities. Laymen will become cheesed off with the incessant name dropping, from Shania Twain to Stephen Jay Gould, which is no doubt already making this book seem dated.
Avoid.