I love this series. And I found the lecturer very captivating. It's a little bit dated at this point, but if you'd like a deeper understanding of the theoretical underpinnings of string theory or m theory, this series explains the theoretical aspects of the series, but excludes almost all of the math. I do recommend that you watch it on video however, because he uses quite a lot of slides. Having listened to the audio, it's not quite the same. And I had to revisit topics. Though this is a lecture series you could probably listen to several dozen times because the material is really dense.