The word choice -- or diction -- in Langston Hughes' poem "Harlem" seems to me to be very straightforward. The poem uses very few words -- maybe even just one, "syrupy" -- that are over two syllables in length. Most of the words, too, seem very concrete; the most abstract word in the poem is probably "deferred."
This straightforward, concrete word choice may have the effect of the making the poem seem very easy to read and to understand. In actuality, the metaphors that fill the poem use concrete words yet suggest meainings that are somewhat difficult to pin down.