While I support the GEB being on here... It's ~750 pages ;)

Gleick is great across the board, and Feynman's life + writings are a great choose your own adventure, regardless of your background. I personally really enjoyed "Perfectly Reasonable Deviations from the Beaten Path" (collections of various correspondences throughout his life, put together by his daughter). Probably more enjoyable with a bit of the context from watching interviews/ lectures or reading "Surely You're Joking, Mr. Feynman"

I never got into GEB, but friends/others loved it. Struck me as a put done/pick up book. I didn't have it at hand and only remembered it as a roughly 2-3" paperback :-).