Whitman’s poetry is much more free-flowing where Poe’s adhered more to strict form. Poe seems to care very much about the aesthetic effects of his poems. Whitman is also much more specific - although he deals with the abstract, he provides a lot of images that are probably grounded in his experience.
In Poe’s poetry (The Raven) there is a sense of melancholy, darkness, hopelessness, whereas Whitman’s Song of Myself is much more positive and optimistic (although topics as death, suicide are present as well). The Self in Poe is powerless, while Whitman celebrates it – and considers focusing on it the best way to deal with any trouble life has to throw at a person. What makes Poe’s style distinctive in The Raven is the number of onomatopoeic words and lines. Whitman, on the other hand, likes to use anaphoras a lot - even though his poem is written in free verse, and therefore there is no strict pattern, the anaforas create some kind of a rhythm. The only two tools to create discernible rhythm are anaforas and enumerations.