Whereas Poe adheres very strictly to classic structures and forms (such as the sonnet) and his poems have typically have a very prominent regular rhythm (i.e. “The Raven”) and rhyme scheme (or rhyme generally), Whitman’s free verse, while certainly not devoid of rhythm or assonance, does not work with rhythm or sound in a regular way. This transgression of typical structure could in itself be interpreted as an attempt to present “raw thoughts” in the form of poetry, the lack of constraints allow Whitman to unite content (idea of the ever-expanding universe) and form (the ever-expanding poem). Poe on the other hand used traditional forms to achieve his aesthetic ideals of a meticulously composed work of art (that is not to say Whitman was not meticulous, of course he kept editing Leaves of Grass until his death).
Both poets deal with death in different ways. Poe views death as a loss (something being removed from the world). His poetry is clearly very pessimistic about the concept, often even adding supernatural elements, which, it could be argued, serve to portray death as something unnatural (of course this could partly be due to Poe’s focus on early death).
Whitman, however, views death as a transformation of one state into another: “All goes onward and outward . . . . and nothing collapses“. Death is then only a part of “nature” or the universe itself, as much as life. His view could be interpreted as optimistic, simply due to the celebratory tone of the poem as well as the lack of elegizing (in comparison to Poe).
It could be said that Poe views death through the lens of the past, as exemplified by the mourning mood and his adherence to tradition, and Whitman also in both content and form, looks to the future.