Stanley Fish's book Surprised by Sin: The Reader in Paradise Lost claims that Milton's poem alternately seduces and chastises the reader, thus "surprising" the reader with a discovery of their own sinful proclivities. The Satan character is so persuasive and attractive that the reader is lulled into admiring him, and then chastised by the epic voice which reminds us that Satan is a rebel whose "vaunting" we should not heed. We then go back and read Satan again, noticing this time not only the masterful rhetoric that drew us in but also the slippages in logic and truth that denote him "the father of lies." Paradise Lost, Fish says, is not only about Christian heroes but it also creates Christian heroes out of the imperfect readers who, then, become the perfect readers.
Fish argues that Milton values logic over rhetoric, which is why the Satan character is passionately rhetorical, while God is coldly logical: "Rhetoric is the verbal equivalent of fleshly lures that seek to enthral us and divert our thoughts from Heaven, the reflection of our own cupidinous desires, while logic comes from God and speaks to that part of us which retains his image." We can see Adam and Eve's fall into sin as their language becomes more redundant, equivocal, and metaphoric, while the language of Heaven is supposedly pure and perfect in which each word only refers to one referent.
A lot of people disagree with Fish because he takes such an outrageous stance, trying to redeem the poem from its flaws and blaming the reader instead. A really detailed (and thus really long) review of the book is here, written by an academic who self-publishes on his website and appears to be an Empson fan. Empson, by the way, took the opposite tack as Fish and said, "If you praise Paradise Lost as the neo-Christians do, what you are getting from it is evil."
I love Milton, and I love Paradise Lost, but I don't know yet if I would go so far as Empson or so far as Fish. Lucky for me, I don't have to make that decision; I can just enjoy the poem.