It's on tv every year so you grow up with it. The comic strips kind of a depressed humor. The cartoons, the originals at least, have Vince Guaraldi's jazz in the background which is definitely part of the feeling. Simple aesthetic. Doesn't feel rushed. The Christmas and Halloween ones are the big ones. There's a Thanksgiving one too I think.... And probably Easter. And some other crappier ones.
It's kind of a Wonderful Life, every person, self-deprecating/depressed humor thing.