Pratchett's Discworld is probably the most popular humorous fantasy series in English. (I do mean "English", as opposed to American.) As the series overview in the books themselves says, despite taking place in a completely different universe, they often comment on real Earth issues. That's my complaint about some of them, that they're too on-the-nose and read like inexpert Swift essays, rather than funny novels with a point.
That does not apply to Small Gods.
I found Small Gods funny and involving both. The novel deals with the empire of Omnia, which might be the answer to the question, "What if the Borgia Popes had ruled the Roman Empire?" It's a purely religious state run by high priests, divided into dioceses run by bishops, and so on, and it's aggressively monotheistic. Our Hero is a lowly perpetual never-promoted novice. Without giving any of the plot away, the story is about the travails of the god Om, and his followers, when worship stops being about the actual god. There are memorable characters, memorable settings, really thrilling adventures, and it's really funny. You can't beat that for the cost of a paperback book. I've only read eight or so, but to date this is my favorite Discworld book.
If you're curious, you could, you know, buy it from the link above. Not that I'm crass or materialistic or anything.