Okay, here's my review.
What it is
"Requiem for a God" is an event book aimed at helping DMs explore the implications of a god dying in their campaigns. It attempts to cover a variety of possibilities regarding the whys and wherefores of such an event, discusses some possible societies that could arise following the death of a god, and it deals with the effects a god's death can have on its worshippers.
(does that make any sense?)
And then, the review...
The new concepts introduced in this book are very creative and they have a pretty high "cool factor," for the most part.
To start with, we get two chapters that basically discuss staging the event and preparing for it, along with a few of the ways a god can die, what can happen after its death, etc. It handles ways to introduce the god's death to the PCs, introduces two opposed societies (the Cabal of the Dirge and the Memento Mori) who take a deep, personal interest in what happens after a god dies, and it offers several ways of handling clerics and other divine spellcasters in the wake of their god's death. There's plenty more, too, some of it dealing with what happens right at death, what lingers behind with the god's corpse, etc. Nice stuff.
Towards the end of this section, we get to the part everything else seems based on: the god's remains. Godsblood and Godflesh is introduced, among other things. It goes over what happens to all that divine power once the god that held it isn't around anymore, with some interesting results. For instance, what if a spellcaster staked a claim near a god's resting place and could somehow...tap into some of the lingering divine energy? What if someone decided to perform a massive ritual to try and personally take over the dead god's position in the deific pantheon? Things like that. We are also provided with sample NPCs (which take up a very small amount of space--surprisingly small, in fact) belonging to the societies.
Then we get four prestige classes. You've all seen the table of contents, so you know what they're called. My favorite was the Disaffected, fallen divine spellcasters (not necessarily clerics and paladins of a dead god; any former divine spellcaster could join the class). They learn to tap into ambient divine energies to cast spells, basically, but they still have a different "feel" from a regular cleric. This is no mere "fix" to handle the problem of a fallen cleric's CR; this is a nice, well-thought-out class that stands on its own.
Next come the feats. The chapter title, "Godsblood Feats," seems somewhat misleading, since not every feat in there is a godsblood feat. Basically, the godsblood feats are abilities you get from infusing yourself with godsblood. This reminded me of Wagner's opera "Sigfried," where the titular hero slays Fafnir, who was in the form of a dragon at the time, and bathes in his blood, gaining invulnerability and the ability to understand the speech of birds. If you take this concept, but make it appropriate to D&D, you have the way godsblood interacts with characters.
The spells chapter was a mixed bag. Some of the spells are really cool, and some of them just didn't interest me.
The magic items were good, but they leaned more towards the utilitarian side of things, rather than the POW, KAZAM, WHIZ, BANG stuff I was hoping for. Actually, I could say the same thing about many of the spells. They're good ideas, solidly designed and functional, but nothing really grabbed me. Basically, the magic items are there for consistency: these are the things you will end up with if you use the other concepts in the book. There wasn't much in the way of "above and beyond" in this chapter.
Again, I was somewhat disappointed by the monsters chapter. I was hoping for a little more power in the creatures, I guess. The divinely infused creature template is pretty good, and not unbalancing if used properly, and the godflesh golem is an interesting idea, but the other two creatures are too weak for what they are, I guess. I don't know; I just wasn't too excited.
The book ends with a series of adventure ideas, some of which are excellent. My two favorites were "The Priests of Grief," a low-level adventure dealing with fallen priests who are trying to bring about an apocalypse, and "The Haunting of the Demiurge," where the PCs are quested by the lingering spirit of a dead god to fulfill a promise it once made. Both of these have great potential for expansion, or they could be glossed over into "side trek" style adventures.
Overall, the book is excellent. The design is solid, and it's well-organized and creative. Throughout the book, there are helpful bulletted sidebars and checklists to aid the DM in planning his version of the event, which was a plus. The worst I can say about it is that some of it just didn't excite me. At the purchase price it's practically a must-have, just for the ideas. In print, I'd probably buy it after a couple of months.
Hope that helps.