"Paradise Lost" fits the description of an epic poem. The specific quality that characterizes an epic poem was first brought by Homer, and its style is that of a long narrative that tells of social preoccupations, events, historical changes, or cultural occurrences that affect a larger population.
Another unique characteristic of the epic poem is the use of language that is complex, elegant, and nostalgic. It is meant to relate major events that, in a quite sordid and laconic way, are now part of history, and shall never be forgotten.
In "Paradise Lost", the theme of the loss of Paradise, or the loss of the grace of God through the dismissal of man from Eden, permeates the narrative. Additionally, the discussion of the Will of God versus the Will of Man gears demonstrates the dimensions of the topic at hand: It is a universal subject that affects all mankind as a whole. This latter characteristic is precisely what distinguishes Milton's poem as an epic one.
Therefore, the use of language, the significance and scope of the central theme, the universality of the audience, and the nostalgic and moralistic characteristic of the narrative are the main factors which make John Milton's "Paradise Lost" an epic comment.