Rose is Rose could be described, perhaps, as the good twin of Calvin and Hobbes. The basic plot is a young child (Pasquale), switching between fantasy and home life, and the occasional real world concerns of the child's parents. Although, as its title would suggest, Rose is Rose is as much about the mother of the family as it is about the child.
In addition to the similarities in plotting, Bill Waterson and Pat Brady have very similiar drawing styles. Although they are (like all comic strip artists) very good at producing imaginative, overexagerrated caricatures, they also have a very good realistic idea for perspective, and, when neccesary, proportion. They also both slip in some very nice landscapes on occasion.
Even Pasquale's constant fanciful wonder of the natural world is very close to Calvin's constant experimentation. Of course, Pasquale lacks some of Calvin's inventiveness: he has a dreamship, but would never be sharp witted enough to turn a cardboard box into a transmogrifier.
Of course, there is one obvious difference between the two strips: while Rose is Rose is almost always sweet hearted, and Pasquale is totally well adjusted and happy, Calvin and Hobbes is, well, Calvin and Hobbes. Although I think that just as Calvin and Hobbes never became downright meanspirited, Rose is Rose never becomes downright sappy and syrupy. Both comic strips are in the end about the wonder of life, just with slightly different shadings attached to it.