I have to file this under "For Heller Completists Only". Like all of his other novels, it's fantastically written. It's funny and caustic with moments of great satire. However, unfortunately, there's a significant amount of dull retelling of some of the Historical books of the Old Testament. This aspect really slows down the pace of the story.
I like to think it's a commentary on the droning nature of the Bible's storytelling. When seen as a fantasy anthology, the Old Testament can be rather tedious, and some of that dullness has seeped into "God Knows". If it were condensed to half its length and focused mainly on David's relationship with his wife Bathsheba and his son Solomon, it could potentially be an outstanding read. David's frustration in his conversations with his rather dim-witted son is truly hilarious, and their exchanges are enhanced by the knowledge that Bathsheba insists on Solomon succeeding David as king. But, unfortunately, those engaging conversations don't make up a large enough portion of the text.
Heller's use of modernisms provides humorous juxtapositions to the "thees" and "thous" of the Bible. Some of the anachronisms, such as multiple references to Shakespeare, didn't quite resonate with me, though. While I can accept his use of "fuck", I have difficulty understanding why elderly David, as the narrator, references events thousands of years in the future. On a positive note, David describing one of his wives as the ur-WASP is quite clever. Overall, it's often a great read, but it's a bit of a mixed bag. An Old Testament scholar with a sense of humor who doesn't study the Bible as a strictly religious text might very well love this.