“I quickly found myself bored by the shiur and left after about fifteen to twenty minutes”.
Wolf, I’m not with you on this one. First, the shiur was not so off the topic; they both dealt with Ishus. It’s not like the shiur was supposed to deal with Pesach but was changed to the Halachic Status of the Mustache.
Also, a good magid shiur/darasha should keep your attention no matter what the topic is and a bad one will put you to sleep, no matter what the topic is.