One of the many Disc World books I missed on the first time through, Small Gods follows the last believer of the Great God Om on his journey to Ephebe and back. Om is about to cease to exist, due to nobody believing in him any more, and, due to a small miscalculation, or perhaps the universe's sense of humor, is in the form of a small tortoise.
Although bordering on blasphemy much of the time, the book manages to be both very funny, and rather insightful about religion - or, more accurately, the organizations that surround religion.
A must if you're a Pratchett fan, but probably give it a miss otherwise.
Interesting take. Small Gods has always been one of my favorite Discworld books, and I think it's one of the more accessible ones for people who aren't already fans.
It's one of my favourites because he tackles a more real issue rather than retelling a fairy tale (or maybe I don't know the fairy tale he's retelling). After a while the notion that destiny/fate is an evolved tendency for reality to tend towards stories (much to Weatherwax's dislike) becomes repetitive, though still making for good reading.
I also liked that Small Gods was outside of the normal plotline, being earlier in history.