H. G. Wells was one of the originators of science fiction. This is one of his minor works, but it's quite clear why Wells was such a master. Food of the Gods is by turns terrifying, insightful, and hilarious.
This is one of the strange old classics of fantasy. Ignore the first few pages -- they're a crappy little framing story, and Eddison quickly forgets about them altogether.
After that -- the grand struggle between Witchland and Demonland is a beautiful and subtle epic war, full of grandeur and subtlety.
It's a touch challenging to read, but absolutely worth your time.