There are much better treatments for many of the individual topics that the lectures cover, in part simply because later textbook writers could see what Feynman had to say and improve on that. There's also the fact that the Feynman Lectures are half a century old. TL DR Feynman's books weren't very useful for self-teaching, brilliant for gaining a deeper understanding after I looked elsewhere. A lot of Chapter 1 and some of the quantum stuff in 3 are very impressive in how much he can show you with relatively simple mathematical tools.

The sections on relativity and spacetime made little to no sense to me when I first encountered it, but I now think his treatment of energy-momentum four vectors is one of the most savvy I've seen. However, upon returning to them after a more 'conventional' treatment of the material, it is immediately clear how brilliantly constructed the material is, and really helps to form physical intuition after you've gotten the dirty mathematics and standard definitions on the topic someplace else. I remember reading about a Caltech student saying that the lectures Feynman delivered were brilliant and intuitive for the duration of the lecture, but basically irrecoverable afterwards - and I feel the same way, his beautifully formed ideas in my head basically collapsed without the glue of intuition to hold them together. His arguments were just too slick for me I could just about follow the mathematical argument in his derivations and proofs, but I didn't have the necessary physical intuition to fully understand how things fitted together.

I continued reading his lectures throughout my undergrad degree in hopeful preparation for courses I would take, but they didn't help much either. The summer before I started college, I read through most of Feynman's first volume, and it was fun reading, but I got as much out of it past the first 20 chapters as you would expect someone fresh out of high school to get, not that much.

Richard feynman lectures on physics