I would prefer not to assign a rating for these books since the rating depends on how one wishes to use them.
As complementary material for an undergraduate degree course in physics I would give them a five. As text books, I would give them a 3, which is my rating here since I have used volume 3 as a text book for a quantum mechanics course. The way Feynman introduces quantum mechanics is very non-traditional though I can see some advantages towards introducing the concept of an amplitude as soon as possible. However, the lack of any accompanying questions and the paucity of mathematics makes this a rather weak text book. Furthermore, Feynman has an annoying habit of defining and then redefining the same quantity in the same chapter. To use it as a text book means the teacher has to do far more work (eg coming up with relevant questions and proofs) than should be necessary.
Furthermore, it is a hallmark of these books that Feynman strived to find new ways to present undergraduate physics. This is useful and admirable though does not necessarily lead to a better way of teaching physics. Teachers are typically "borrowers" - well I am anyway. If I encounter a good way of explaining a concept, I'll absorb it and use it in my teaching. Only some small parts of the Feynman lectures (Vol. 3) have found their way into more recent text books; this indicates that teachers don't find them pedagogically superior to existing material.
The near universal 5 star rating for these books puzzles me. I wonder how many reviewers would have given five stars if, when they encountered the books for the first time, the books were called "The John Smith Lectures on Physics".