Well, they weren't what I signed up for when I was a kid. I wanted to see a kid having fun being a kid, travelling through space and riding dinosaurs. Not a surly grownup talking through a kid.
In a way Calvin was growing up and becoming a more introspective and thereby pessimistic person growing into young adulthood, leaving his carefree days behind. At least that is what I took from it. Then the last panel, if I remember correctly, was an ode to the carefree days of childhood.
