I think Vol. 1 is really masterful. I read somewhere Feynman was most pleased with Vol. 1, and less so with Vol. 2. The material in the second volume is certain

I think Vol. 1 is really masterful. I read somewhere Feynman was most pleased with Vol. 1, and less so with Vol. 2. The material in the second volume is certainly more difficult, and I did not quite finish it myself. I've been busy with other things, and the relatively thin Vol. 3 still sits on the shelf.