Milton's tone in Paradise Lost can be described as elevated and mournful—his invocation in Book 1 laments the "mortal taste" of the Tree of Knowledge, which "brought death into the world, and all our woe."
While Milton clearly sides with God/the Son of God/Adam over Satan—who tempts Eve to near-ruination—he also expresses an understanding of and interest in darkness and evil: rather than issue a blanket disavowal of sin or immorality, he acknowledges that it is part of the human experience (and has been since the fall of man), and therefore necessary to examine closely: "what in me is dark/Illumine, what is low raise and support/That to the heighth of this great argument/may assert Eternal Providence/And justify the ways of God to men." This makes his tone more nuanced, analytical, and balanced—defying the rigid precepts of Judeo-Christian moralism in favor of a more complicated perspective.
For that reason, Satan is sometimes depicted in what might seem like a flattering light—as a charismatic orator capable of experiencing many different emotions (regret—which he momentarily experiences before tempting Eve—envy, sadness, and anger). God, by comparison, is utterly unemotional (his role is merely to hand down divine justice), and seems less fleshed-out—indeed, he first appears in the poem as a dazzling streak of light.
