I have listened to all of the Feynman lectures at least a dozen times. This set is typical.
In order to get all of the Feynman lectures you need audio volumes 1-19 (volume 20 is all repeats) plus you need Six not so easy pieces. Even then you will be short a handful of lectures.
All of these lectures are from the three volume printed set of lectures.
1 3,9 02/24/63 9. The Ammonia Maser
2 3,10 05/09/63 10. Other Two-State Systems
3 3,11 05/13/63 11. More Two-State Systems
4 3,18 5/25/1964 Angular Momentum
5 1,33 03/06/62 33. Polarization
6 2,19 03/17/63 19. The Principle of Least Action
1 1,34 03/16/62 34. Relativistic Effects in Radiation
2 1,6 10/13/61 6. Probability
3 1,07 10/17/61 The Theory of Gravitation
4 2,1 09/27/62 1. Electromagnetism
5 2,42 04/11/63 Curved Space
6 3,02 (1,38) 04/06/62 The Relation of Wave and Particle Viewpoints
These lectures are from the first freshman course and are fairly easy. Feynman makes Work and Potential Energy a bit too hard and then decided to do a new lecture that would be easier to understand for his freshmen.
These were recorded in 1962 on 1/4 inch audiotape at 3-3/4 ips. There were frequent problems with cables clicking and there were noises especially when the lights were turned on an off in the classroom for various experiments.
It is often difficult to follow without seeing the written lectures, and sometimes with the written lectures, because Feynman changed the notation frequently in the middle of a lecture. He always got the algebraic sign wrong and told the students to figure it out because he did not personally feel the signs were important enough to worry about.
There are some curious things in Feynman's lectures you don hear much about in physics lectures today - such as the component of a radio wave that goes as1/r instead of 1/r squared, and a lot of worrying about the delayed field due to the speed of light.
Having said all that, these lectures are enjoyable, especially if you are collecting the whole set.
My gripes are that the publisher has released 20 volumes with about 20 duplicate lectures in those sets and yet there are still a handful of lectures that have not been released.