Very nice couplet, although there are dull stretches.
Shakespeare wrote his sonnets within a strict discipline, fourteen lines of iambic pentameter, rhyming in three quatrains and a couplet. Were his sonnets dull? Mozart wrote his sonatas within an equally rigid discipline - exposition, development, and recapitulation. Were they dull?.
Then, at the last and only couplet fraught With some unmeaning thing they call a thought, A needless Alexandrine ends the song, That, like a wounded snake, drags its slow length along.