Accessible to anyone who can sum a geometric series and take a Fourier transform!
(Feynman diagrams for dummies basically, for any who run across this comment - yes I’m being cheeky about “dummies” but I believe it calls itself something similar in the front matter. A self interaction term, then.)
Feynman's own book 'QED: the strange theory of light and matter' is another good read, but strangely it is a bit lacking in illustrations. (And the illustrations that are there are a bit dry compared to Mattuck!)