Much of it is favourable, even admirable, and even accounting for a certain rosy view it sounds like a great time and place to grow up. As long, that is as you were white - there are some truly distressing accounts of horrific racism and racially-motivated murders.
The book does become darker as the era progresses, as the era did itself. There's a strong emphasis on the prevalence of Communist fears: "It was an especially wonderful time to be a noisy moron.... Although he had no qualifications (he had flunked out of Ozark Bible College - a rare distinction, one would suppose), Hargis founded several educational establishments, including the Christian Crusade Anti-Communist Youth University, (I would love to hear the school song.)" Some of the rampant, mindless anti-Communist measures echoed for me the current hysteria about terrorism, with politicians advocating for the suppression of human rights if doing so stemmed the threat of Communist encroachment. Bryson tells of Dr Ernest Chain, a Nobel prize winner for his work developing penicillin, being refused entry to the US because he had - at the behest of the World Health Organization - helped set up a penicillin plant in then-Communist Czechoslovakia, and famed chemist Linus Pauling (who would himself be awarded the Nobel prize, twice) was prohibited from leaving the country "on the grounds that he had once or twice publicly expressed a liberal thought."
Although I've enjoyed other of Bryson's works more, I left The Life and Times of the Thunderbolt Kid more informed and with a better picture of the US than I expected. I heard Bryson speaks a couple of years ago, when he was in Australia promoting the release of the book, and he was as engaging in person as he is on paper. - Alex