So four panels usually follow what I call "limerick timing". First panel builds a premise, second and third add energy to the premise, the fourth panel has less energy and turns everything on its head.
I call it "limerick timing" because a limerick enforces this kind of rhythm with its syllable counts. The shorter the line, the more often you hear a rhyme, the more energetic the verse is. So the energy goes medium-high-low.
Almost every comic uses "limerick timing". The biggest exception that comes to mind is "Jim's Journal", which has an anti-humor kind of timing I call "fizzle timing". Sometimes someone will make a declaration in the second panel, and the third and fourth panels are just the two characters staring motionless at each other.
What you have to make your peace with is that, if you're doing the same thing again and again (making a four panel joke with the same characters), you're going to kind of do the same thing again. Bill Waterson is a genius. That most Calvin and Hobbes comics are Calvin making a point more and more strongly only to have his point refuted by Hobbes in the last panel doesn't take away from that. It's the nature of the medium.
