This book is exceedingly ambitious, attempting to explore the circumstances under which the existence of God might be scientifically provable, by positing such evidence in a science-fictional setting. It does well as fiction. However, it does not do justice to god or science. To the same extent that two out of three isn't bad, one out of three is bad. It is so bad, in fact, that I am tempted to conclude that it was actually written as some sort of twisted joke. This is milder than the alternative, which is that Mr. Sawyer buys the arguments for intelligent design and thinks that putting them into the mouth of a fictional paleontologist will make them more convincing.
I will spoil, hard. This shouldn't be a problem, as I recommend that you do not read this book. The two main characters are paleontologists: a human, Dr. Jericho, and Hollus, a Forhilnor.
I like all of the aliens that actually get any lines, both as individuals and as alien concepts.
Dr. Jericho's internal issues around mortality are solid writing.
The prose style is solid and pleasant.
First, to get it out of the way, the side-plot with the abortion clinic bombers is abominable. This is far more of a farce of believers than the portrayal of Dr. Jericho is of skeptics, and that's saying quite a lot.
Second, the 'god' in this volume is not God by any commonly understood definition of the word. This god was created by natural processes and is entirely constrained by the rules of the universe. It wields no moral authority. It has none of the three conflicting criteria from the Problem of Evil: omniscience, omnipotence, or omnibenevolence. It is extremely smart, though it seems to fail to see quite a bit; its power is likely at least Kardashev 2 (has available the mean power output of a galaxy), but definitely not a Kardashev 5 (has available the mean power of the whole universe); and we can't be sure that it isn't just self-interested. Certainly it thought that continuing its own existence was worth causing cancer to ever exist. Such an entity is definitely worth knowing as much as you can about; it is not God.
And so, the argument is framed entirely wrongly throughout the book. The nature of our popular conceptions of god and gods would be clear to the Forhilnors, who have seen a decent amount of our TV. So, it would be clear to them that they cannot just say 'God', meaning that thing, and expect to be understood. Yet Hollus does expect that. It is this misunderstanding which forms the crux of the book. Just as you shout at the people who dumb things in horror movies, I found myself shouting at both characters for not getting this clarified, as they argue over the existence of this powerful entity on the one hand, and the nonexistence of God on the other.
This dissatisfaction reaches a climax at the end of the book when Dr. Jericho essentially has a religious experience relating to this being. Its nature remains totally unexplored. The pace feels rushed here. If it had been explored more fully, this whole issue could have been resolved. This kind of writing is very difficult, so it is easy to see why it was not included; however, if you do avoid writing it, it is best to avoid situations where you need to write it.
Third, the reaction of Dr. Jericho to the essentially irrefutable proof of some kind of intervention: the unexpected genetic overlap between two alien species and humans. This genetic overlap is specified to include genes oriented towards multicellular life, so it cannot be caused by monocellular panspermia. Any rational person would at this point accept that some intelligent force intervened in our development. The rest of the debate would simply devolve to whether we should call such a thing 'god'. The only reasonable conclusion given these characters would be to, in a matter of a page or so, decide that it's all right to disagree on that definition.
However, Dr. Jericho refuses to accept this line of reasoning, and the only explanation I can see here is sheer stubbornness. Given the level of evidence provided, I suspect that Richard Dawkins would provisionally accept the idea that we did not develop in isolation. So here we go, having a little joke by portraying skeptics as dogmatic. How tiresome.
Here, as in many other places, positions are completely overlooked which would throw a monkey wrench into the argument. No one puts forward the idea that some first ancient species spawned all the later ones (which is kind of what happened, but without theological overtones). There are things that Hollus could have countered with, but Dr. Jericho didn't even think to ask.
Fourth, there are the philosophical errors. The Forhilnoran theory of everything is deeply misused. It states that the universe is finite in size, and only gets seven chances to achieve the parameter fine-tuning necessary for life. It is raised to make the answers to the fine-tuning argument not apply to this fictional world. This is structurally necessary to the story, so as to make this god's powers more godlike. However, it is treated as a principal argument in favor of this being's sheer existence. Its use in this case is silly. Why? Because the argument is fundamentally flawed: this theory says there is nothing else.
The problem is, the best this theory can achieve is to eliminate the very good reasons we presently have to believe that there actually are other modes of existence. There nonetheless remains no reason whatsoever to conclude that the only existence is with the same laws we have. Opposing such a supposition would be an excellent position for the Forhilnorans to take, stating that they are not in the habit of wild speculation. But instead they take the extra step and make the opposite and equally speculative assertion that there is nothing else, and pretend it's been confirmed by experiment.
It is not merely subtle issues of the philosophy of science that are flawed, though. There are straightforward errors of interpretation. For instance, the discovery of super-massive exoplanets is taken to prove that systems like our own are downright rare. Never mind that super-massive exoplanets are the only sort we were capable of seeing at the time, so it isn't at all surprising that we have only seen them, even if systems like ours are common.
And so we have a Jericho who ends up swallowing all of the intelligent design arguments that even come up, even though the validity of most have not been changed in the least by the sudden introduction of our fictional evidence (indeed, some of the fictional evidence goes against these arguments, due to the prevalence of life which very well may not have been as directly influenced by this 'god' as we were). If this book had been an action adventure, it would not have been a serious issue at all. But in a philosophically-oriented volume such as this, it is utterly crippling.
Fifth, the error that had me half-convinced that this is actually a farce: most aliens, it seems, when they develop the appropriate technology, reimplement themselves in computers and let their physical bodies die off. These computers are universally stowed in some vault, and bear passive defenses made of rock. Period. They cease to interact with the outside world. They do not build robot civilizations. They do not even build active defenses to protect their vault. They do not produce any noticeable response when other aliens land and inspect the outside of their vault. They become totally inert.
Now, really, Mr. Sawyer. I could buy one alien species doing that. But all of them? You're referring to a technological singularity. I've read multiple books set during and after such a singularity, by multiple authors. Not one of them have this stupid an arrangement. Even The Matrix had the computers running an active civilization up on the surface.
Sixth, the error which is essentially emblematic of the book. The rules of Conway's Game of Life are misstated, such that no interesting patterns would emerge.