The first ever collection, with an intro by Charles Schulz. Who recounts how he wishes he had had the idea after reading one of the comics. . . .
You can see the art evolving throughout the book, though it seems to have reached its final form, more or less by the end of the book.
It also opens with Mooch and Earl not knowing each other. After a few comics where they eye each other, they seem to have actually become friends off panel, since it shows them showing each other their homes.
It has classic bits, like the time Mooch asks Earl why bees keep busy, a brief retelling of Goldilocks with both Mooch and Earl taking the title role, and a sequence revolving about a caterpillar becoming a butterfly.
It also introduces repeating characters, like the butcher, the bear, and the guard dog. Though they aren't entirely formed yet, some of them. (There's a sequence where they think they are facing the guard dog.)