Try reading "Richard Cory" aloud. Go ahead—we'll wait right here while you do.
Not much exciting going on there, is there? It's written in good ol' iambic pentameter, without many variations, and it's got a solid ABAB rhyme scheme. (See "Form and Meter" for more on this stuff.)
The lack of variation in the meter and rhyme are mirrored in the comparative lack of sounds popping off in this poem. Sure, you get some mild alliteration in lines 2 ("people," "pavement"), 12 ("wish," "we were"), and 13 ("we worked," "waited"). And there's some assonance with the short U sounds of "fluttered pulses" (7).
Mostly, though, there's not too much to jump out and bend your ear. That unremarkable-ness, though, has a profound effect. It actually adds to the huge blow that hits us at the end of the poem: Richard Cory's suicide. Everything in the poem is very "la di da, la di da," and then BAM. We learn that Richard Cory kills himself. The contrast between how the poem sounds and what happens in the end really drives home the poem's final revelation.