Mencken's childhood memories are wonderful for two chief reasons: as excavations of the lost world of comfortable German-American Baltimoreans of the 1880s, and for the incredible vigor that HLM got into his prose.
HLM is, I think, more notable for his talent as a sentence-crafter than to any claims to wisdom, and we are treated to some beauties:
On his baby fat: "This adiposity passed off as I began to run about, and from the age of six onward I was rather skinny, but toward the end of my twenties my cross-section again became a circle, and at thirty I was taking one of the first anti-fat cures, and beating it by sly resorts to malt liquor."
On his father's (who owned a cigar factory) professional palaver: "They fell to talking of the illustrious personages they were constantly meeting in Washington - Senators who had not been sober for a generation, Congressmen who fought bartenders and kicked the windows out of night-hacks, Admirals in the Navy who were reputed to be four-, five- and even six-bottle men, Justices of the Supreme and other high courts who were said to live on whiskey and chewing tobacco alone."
These quotations capture the spirit of Happy Days - cynical and critical, but pleasantly entertained by the faults of the world. It's a deeply conservative mindset. HLM critiques not because he wishes to revise the world, but because there is so much entertainment in doing so. The pleasure in reading Happy Days is only alloyed by his treatment of blacks. While I wouldn't expect Mencken to be politically correct (or even generous), it is fair to expect him to have been as critical and clear-eyed towards racial stereotypes as he was towards most things. Afterall, Mencken did famously excoriate the Klan when it surged in the twenties. He was not a standard-issue bigot. Instead, Happy Days' frequent accounts of young HLM's black acquaintances do little to rise above pernicious southern tropes.
(I read this one in the Library of America's collection of HLM's memoires, which includes his appendecized revisions - "Days Revisisted." Days Revisited is probably only required for the completist who needs a list of every one of HLM's childhood neighbors and the history of their progeny, eg, but it is a useful account of which of HLM's relatives he believed were stupid, nincompoops, idiotic, etc.)