I've been listening to these lectures (one per book - a total of 6 separate videos) and he mentions in part 2 (on book 2) that there appears to be a missing section of the text, because it skips suddenly to speaking about the gods. It's possible that this is most observable in the Latin text - have not located the section yet (not able to read Latin, and tried finding it in the English translation at the Perseus-Tufts site).
I think these are very good lectures, as I've only skimmed parts of Lucretius, and so this helps flesh it out.