I've been reading this essay diligently of late, and have borrowed a passage for use in the most recent recording for EpicureaPoetica (which, by the way, I hope to publish this afternoon).
Santayana was a Spanish-American philosopher of a Platonist bent, and his depiction of Epicurus won't win him any friends here. He slightly echoes Nietsche in this regard. Nevertheless, I think him a deft and engaging critic of Lucretius, whom he does hold in high esteem. Those who have a good foundation in the core texts—of Epicurus, of Lucretius, of Frances Wright, and of DeWitt—will be well-served by reading it.
My intention in the coming days is to draft an outline of the essay, so if you'd prefer to save some time you can wait for that instead. A straight recording of the essay may follow. He doesn't mention Tennyson's poem, but he has shed new light on Tennyson's approach to Lucretius, by outlining his own.