Truth is a soundless gong
By an altar black and cold;
Life is a tale half-told,
Love is a broken song;
Beauty, besought so long,
Is a legend lost and old.
This is a dark little verse, but what captures my attention is the strong ABBAAB end rhyme scheme, a sort of variant of the more familiar enclosed rhyme pattern ABBA. All of the rhyming words at the end the lines have a single syllable (in "half-told" only the word after the hyphen is rhymed), which encourages the reader to place a strong beat on each of those words.
When read aloud, "Simile" has a rich sonority, and the combination of alliteration (primarily using the letters B, L, and T) with the end rhymes noted above allows the music in these lines to flow.
Although I don't often dwell on principles of versification on this blog, every once in a while it's worth noting CAS' technical mastery of those principles, demonstrating that his skill as a poet was no accident: he possessed a strong command of the tools of his trade.