Eve's dream is full of classical syntax and references to Classical mythology of goddesses, while Adam's dream has a more homely and humble status, and its beauty is of nature rather than divine images -- it seems, additionally, more consistent with the vision and character of the man, despite his protestations, unlike Eve who seems to directly dream Satan's dreams of light and lordliness over all the world and all the heavens.
Thus, the different qualities of male and female dreaming indicate not only the different ways in which men and women dream of power but also the greater ability of women to be impinged upon in their brains by evil. Adam's dreaming vision is more concrete, while Eve's is located in a lesser sense of physical reality, and lies in the highfalutin syntax and discourse of Satan's twisted mind. Eve experiences her dream almost as if her brain is being raped or impinged upon by outside forces, and her husband experiences outrage and this violation of his helpmate's consciousness much as if it were a sexual act. Adam does not relate his more humble, yet still disturbing, dream to Eve in the same immediate fashion, although he too describes dreaming to himself as a kind of impingement from the outside, rather than a psychological or internal manifestation of his own consciousness, although his dream is more along the lines of a gardener or farmer enjoying the fruits of his labor in an especially intense way, in the way he sees nature around him.
Milton's use of dreaming prefigures what will transpire in the poem's narrative later on, and this may be one reason that the characters of Adam and Eve have a sense of being impinged upon by others -- Milton makes Satan's devious plans quite clear as a kind of foreshadowing, and Eve is the first to dream and the first to fall. In particular, the stress upon divinity in Eve's dreams suggests her greater grip in the hand of evil. She is more subservient and susceptible to the fantasies of Satan than is Adam because she has a weaker female soul, although Adam still loves her and she seems like a fundamentally 'good' person, as viewed by her helpmate in Eden Adam.
The use of dreaming in the poem also serves an important form of foreshadowing, to create narrative suspense. All of Milton's readers would have known what was going to happen at the poem's end. The suspense lies in how the poet will relate this, and how the different characters of Adam and Eve will enter into temptation. The characters of the two are revealed through dreams, the psychology of Satan as manifested in the male and female mind, and lastly the climax of the tale is hinted at, and rendered suspenseful even to the most knowing reader.
Giving forth what will transpire in the form of a dream may have an additional theological component for the poet Milton. If Adam and Eve know what will happen, and are told, despite their expressed fears, that they will fall from Eden, then their fates must be predetermined, despite the generally accepted Catholic interpretation of humanity's fall as an act of Free Will, rather than of determined moral logic. Milton, however, was a Protestant and a Puritan, and viewed human history in the soul not as a tale of Free Will but in a far more predetermined fashion, although he was not an out and out determinist and Calvinist. Eve's purity and innocence, as stressed by Adam, and her mental and moral encroachment by Satan makes her a far more sympathetic character than she is in the Genesis account, viewed against the Catholic doctrine of Free Will and absolute moral responsibility for Original Sin. Thus the use of human being's dreaming imagination and fancy, in "Paradise Lost" has an additional theological component of determinism, as one is impinged upon in one's will by outside, evil forces, and also that of a narrative component, as it prefigures what will occur in fact and reality, in Eden.
Milton, John. "Paradise Lost." 1687. Available online 17 November 2004 at http://www.dartmouth.edu/~milton/reading_room/pl/book_8/index.shtml