In the biblical story on which Milton’s Paradise Lost is based, the various ‘characters’ fulfill clearly distinguished roles that have a straightforward moral value: God is a perfect, good and just ruler; Eve is his disobedient subject; Adam is the gullible husband deceived by Eve; Satan is a despicable villain. Are these roles still as clear-cut in Milton’s epic? Why/why not? Can someone please provide any textual evidence for this?
The roles are not as clear cut as this. Although some scholars will disagree, Milton did draw Satan's character as something more complicated than simply a despicable villain. In fact, Satan is downright sympathetic, even treated as an odd kind of hero in that he refused to submit to God's law. This is evoked in his famous line, "Better to reign in Hell than to serve in Heav'n." (Book I) Of course, Satan's initial rebellion, perhaps sympathetic in the beginning, eventually leads him to become the despicable villain he is more commonly known as. Therefore, his fall goes from rebellion to possible sympathy to complete evil. So, to label him a villain from start to finish is too simplistic, certainly in Paradise Lost.
Also, given that Satan and humankind (Adam and Eve) both had a tragic "fall," we might consider a parallel drawn between Satan and the two he tricked. Since Adam and Eve fell as well (as Satan did), the implication is that they too have the free will to choose to obey God or, as Satan did, to rebel (which of course they did by eating the fruit). And again, although Satan freely chose to go against God, his fall is so far (even further than mankind's) that he is and will always be miserable. Here in Book IX, we do not get the sense that Satan is happy ruling in Hell rather than serving in Heav'n. Rather, he is miserable. Since he sees no prospect of going back (or that he's too proud to go crawling back), he can only find solace in making others fall as he did:
Nor hope to be myself less miserable
By what I seek, but others to make such
As I, though worse to me redound:
For only in destroying I find ease (Book IX, 126-29)
And while Eve is often cited as the one who first ate the fruit (thus the one who "started it" to use a phrase of a child blaming others), Book IX ends with Adam and Eve arguing over who is more at fault. The Book ends without a resolution. Adam blames her for being lured by the Serpent, but Eve replies that if it was his job to be the "man" he should not have let her go off to work alone.
Being as I am, why didst not thou the Head
Command me absolutely not to go, (Book IX, 1155-56)
Here, we don't have a clear cut definition of Eve as the sole cause. In fact, here we have an argument for women to be equal and one traditional argument against it (ironically used by Eve). If Adam is in fact the "Head" of the household (as unequal as that may seem today), and being created with a more intelligent mind, then it is his fault for allowing Eve to go out alone. This is Eve's argument. Here, she essentially says, 'if woman is less intelligent than man, then it is your - Adam's - fault for allowing me - Eve - to go out alone.' So, the fact that Adam agreed to let Eve go makes his reasoning skills as questionable as hers. This is a convoluted but direct explanation that puts the blame on both of them rather than the traditional scenario of mostly or completely blaming Eve.