Very much if it's time and difficult use of language makes this a less than easy read.
Preserve and you are rewarded with strong characters and equally strong characterisation and some vivid imagery.
Eddison was a scholar of Northern Mythology and the title refers to the snake (worm) that early Norse people thought encircled the world.
I'd describe this as a work of early, blood & glory type fantasy. Set on the planet Mercury, the world is recognisably medieval.
There is a strong moral tone running thru the book and non of the characters are wholly bad (or wholly good)
Anyone interested in fantasy as a whole - or interested in looking for where Tolkien got some of his inspiration from - may well find this a diverting and interested book.
I certainly did when I first came across this some 40 odd years ago!