Disclaimer: the publisher has sent me a review copy of the book (in PDF format).
The Gods Have Spoken is a 5th edition supplement with 28 new deities and everything that comes with it: multiple character options (specially for clerics and paladins), holy (and unholy) locations, factions, new monsters, magic items, and a few 13th Age-inspired house rules.
The appearance of this book is puzzling, with a curious mix of good and bad stuff. Most of the art, for example, is very well done (similar to the cover) - but some pieces are repeated two or three (!) time throughout the book, sometimes in adjacent pages (!!). Since the books uses good quality B&W and stock art, I see no reason for this.
The same thing happens with the layout. The overall quality is very good: the PDF is fully bookmarked, with a decent index, table of contents, glossary, and multiple side-notes, but also with lots of empty space. The page borders are not particularly beautiful nor do they have anything to do with the subject of the book , but each chapter is color-coded, which is nice and useful.
In short, it looks like professional work left unfinished. Well, you can judge for yourself:
First of all, while the book doesn't described a complete setting (since this is not the subject), it does imply a fairly high-fantasy setting with dhampirs, gnomes, and probably some steampunk. It fits 5e assumed setting well.
The book describes 28 deities divided in three different pantheons: the Thirsty Gods (of Egyptian flavor among other things), the Old Gods (Celtic, Norse, Slavic, etc.) and the Bright Gods (who might be based on eastern philosophies, although I cannot say for sure).
The deities are all creative and unusual; you never really feel that a deity is just Thor or Bahamut with a different name. The way the pantheons are described is very organic and flavorful: religions change, influence one another, create superstitions and schisms, guide different sorts of behaviors, etc. All of these aspects are described within the book. This is both useful and inspiring, even if you want to use it to create your own religions.
The holy and unholy places of each pantheon are intirguing, with plenty of ideas about encounters, scenes, and adventure seeds.
Then we get the factions. Again, they are diverse and flavorful: not only sects, but artisan guilds, secret anarchist cults, musician warriors, preservers of the faith, etc. The mechanics involving these factions are an important part of the book and will be discussed in the next topic.
The book also has half a dozen monsters (a dozen if you count variations) and a few NPC allies. Fluff-wise, the monsters are very cool, with mythological roots tied to the exploits of the main deiteis. Mechanically speaking, they have a few twists that I'll discuss in the next section.
Finally we have a few magic items and a whole system to generate holy weapons. This part is short but looks extremely useful, even if you don't plan to use any of the deities in the book.
The character options contained within the book are standard 5e: cleric domains, druid circles, paladin oaths, feats, and three backgrounds, one for each religion (well, actually, the three are variations of the acolyte background - and a bit of needless repetition there). A few warlock pacts would be a nice addition. Everything seems fitting and balanced, with a few exceptions. For example, you get some of this:
"You are proficient in survival if not already. As well, you double your proficiency bonus for all survival checks."
This is obviously more useful to someone who doesn't have the proficient already. Compare this to the feats in the Unearthed Arcana: Feats for Skills from Wizards of the Coast:
"You gain proficiency in the Acrobatics skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it."
I'm not sure this is on purpose, because some feats might be too weak without this "free expertise" (Reknarite Knight, for example).
Flavor-wise, the options are very good and fit well with the philosophies of the respective deities. Overall, they are good additions if you're looking for more religious character options.
The book also has an entire faction system, with suggestions on when and how the factions interact with the individual PCs, how characters get favors, information, potions, enmity, etc. This seems to te heavily inspired by 13th Age (it seems the book has an earlier 13th Age "sibling"), but is much more detailed than the 13th Age SRD in this aspect.
If you want to have formalized rules about factions, these will certainly be useful - I am tempted to use this myself for 5e, even if I was never convinced by 13th Age's "Icons". This is another part of the book that you can use even without the deities.
You can also get "allies" with this system, with various functions: some will heal the party, others will hinder enemies, and so on. The "damage sponge" is a peculiar type of NPC who will draw heat from enemies.; the "redshirts" of the setting. The concept of having someone to die for the PCs doesn't seem particularly heroic (for the PCs) or believable, but I can see how it might be useful. Unfortunately, their stat-blocks are strange; a third-tier damage sponge has +12 to hit (which is probably WAY better than the PCs they follow). So, yeah, they will basically look more competent than the PCs and then die first in battle. I'm not sure the players will appreciate.
Monsters also have a few unique features inspired by 13th Age: they get special attack if they roll a "natural" 16 or more on the dice, or if the result is even, etc. Another feature of 13th age I didn't particularly like for PCs, but makes sense for monsters.
The Gods Have Spoken aims to offer more options for PCs and also flesh out the "Religion" chapter of a full setting, and it does both competently. But the book is much more than that. Specially, the faction system has lots of cool rules that might prove useful to any 5e game (or any RPG at all, if you think about it). It is also a good way to test a few ideas of the 13th Age RPG within a 5e framework.
On the other hand, the unfinished look of the layout and a few inconsistencies with the mechanics detract from the rest of the work, and the price ($17.45 as I write this) might be a bit exaggerated for the page count with this amount of white space.
Overall, I feel the book deserves a bit of extra work to become really good, as it shows great promise; however, it has plenty of interesting stuff already, specially if you want more options to play with factions, religions and deities in your 5e games.