Neil Gaiman's American Gods is a Very Good Book. It has excellent dialogue, characterization and an absorbing plot, squarely within the Fantasy genre. (It's not SF at all). To discuss it, I'm going to have to include some mild spoilers, so be forewarned.
Basically it asks what if each immigrant group came with its own gods to US shores, and what if these old gods were still pottering about, living like people with relatively normal lives but with odd magical abilities?
And what if the old gods were being weakened somehow by modernity, disappearing slowly, but trying to fight back? It's an interesting and potentially very fruitful sort of mythic storyline.
The main problem with the plot involves the supposed Huge Upcoming Battle, that pits the old gods and the new American gods of media, the internet, and so on. (The two sides remain somewhat ill defined throughout, particularly the latter side, pitched as more or less evil).
The problem is that there is no conflict between those aspects of modernity and the old gods. Indeed, the old gods should expect to find solace and succor in technological advances such as the blind eye of media and the hyperactive internet. TV doesn't compete with the old gods, it makes them more real. The old gods live quite nicely on the internet.
The actual competition is between the old gods and the newer or better marketed gods of Christianity, Judaism and Islam. The actual competition is between the gods, old and new, and other sources of modernity such as science, skepticism and humanism, thought patterns that conflict with the very notion of gods or the supernatural.
(Of course, a large part of this conflict involves co-optation in one way or another. It isn't ever simply a matter of replacement, not on anything like a global or national scale).
I expect that Gaiman didn't take those latter routes because it would have been more difficult to come up with a compelling narrative -- or the kind of narrative that he found fruitful -- by having a fight between the old gods and Jesus, or gods and the godless. Those would have been very different stories, and to do them right one would have to avoid the morass of cliché that surrounds them.
In the interview section that closes out my copy, Gaiman says he wrote up an encounter between the main character and Jesus, during a scene replete with Christian symbolism. He says he found it "very unconvincing", so cut it from the book.
What results is, again, a Very Good Book, but one that skirts the surface of the issues involved, leaving many of the deepest foundations unexplored.