This is the first strip (or one of them, anyway, I don't remember any others) in which one of the female characters shows unequivocal anger towards Charlie Brown without cause. Later strips would focus on the feelings of the wounded CB in these cases, but here it's just used as a punchline. So even though the subject is similar to modern Peanuts, the strip doesn't yet have the depth of introspection for which people remember it.
If I keep linking every strip like this, we'll be going through it roughly in real time!