Comfy small-town storytelling and wit from the mid-twentieth century midwest. It's the opposite of a thriller, but not in the sleepy sense - it's just good for relaxing and smiling. Lake Wobegon precurses the "slice of life" media genre. So many novels have tension and some sort of dread or important conflict baked into the plot. But Lake Wobegon is too mundane and petty and pious for that.
Perhaps I'm already biased because I grew up with the radio show "A Prairie Home Companion", also created by Keillor, which features similarly smart and small stories from the same fictional town.