I took a course awhile back with a professor who absolutely adored his work for the beauty of his language. We fought our way through Paradise Lost, and she convinced us that it was the beautiful work.
The reasons? First of all, he has a mastery of the sound and sense of the English language that very few people have. He knew his Greek and Latin too, and he would use words based on their original root meaning (for instance a bush having “branches implicit” – literally, “tangled branches”). This often gave a double meaning to some of the things he said.
Most modern readers need very good footnoting to catch these (I’ve found the Penguin edition to be good).
He also invents a number of new words, phases, and uses of old words. “Pandemonium” makes its first appearance here, for instance.
Another reason was his remarkable theology. I’m Wiccan and my teacher was atheist, and the two of us marvelled at how he actually managed to make sense of some of the thorniest issues of Christian belief: how there can be free will if God knows the future, how a perfect God could make Satan, etc. and he does it logically and believably, though this requires him to depart a little from Puritan orthodoxy.
Another interesting aspect of Paradise Lost is the way in which it deals with science. Paradise Lost is all about knowledge, and its place in a human society. More specifically, it’s about science, the newly-budding natural philosophy which had just tossed the Earth out of the centre of the galaxy, and was changing the face of the European world.
Science is everywhere in this book, and Paradise Lost is an interesting snapshot of the changing times. Galileo is mentioned three times, and is the only one of Milton’s contemporaries to be mentioned by name. The literal veracity of the Bible is question (as Raphael tells Adam and Eve, the Bible is explained in simple terms because human beings weren’t ready for the full story).
But gunpowder is here – Satan invents a version of it. And the Tree of Knowledge is called “Mother of Science.” The theme is that science isn’t a bad thing as long as the purpose is to better understand the beauty and wonder of God’s creation. Used without God or morality, it becomes a force of destruction.
(Of course, this is all made ironic because two centuries later, science would declare Adam and Eve to be, at best, an allegory.)
Sometimes you’ll hear the claim that Paradise Lost is the first work of science fiction. Not sure if that’s true, but there is a case to be made for it. Milton did coin the term “outer space” (Satan flies through space to get to Earth) according to the Oxford English Dictionary.
It’s also one of the first books to postulate other star systems in space, replete with alien lifeforms (brought up, again, during Satan’s spaceflight).
I mostly know about Paradise Lost, though he has some other interesting work. In spite of having been official propagandist of the Cromwell regime, he was also known for his passionate defence of free speech.
For more than that, I really can’t help you, though.