One of the very few comics that I read religiously while growing up was "Calvin and Hobbes" by Bill Waterson. This comic was more than just a mere 6-cell joke to me. Within each frame carried art, ideas, and humor that was not contained to the mind of a child. I've gone back and read the comics recently and found out there was a lot of subtleties and references that most younger readers wouldn't understand.
Who would expect this young child to know so much about life? Calvin shows throughout the series that he notices a lot of sociological and psychological issues and makes witty remarks about them. If you look at the strip posted above, it provides a clear example of Calvin's intelligence (click on it to enlarge)
Calvin is in the middle of taking a test and he's writing on his paper what many see as a flaw in the current education system. This ability to see this type of learning habit is not usual for one of Calvin's age.
Another thing I noticed is Waterson's use of speech bubbles, and font to relay information as to where the dialogue is coming from and how it is to be read. In the same comic you can see that Calvin is staring at his test, and in plain font it states the question. This way it obviously states that the dialogue is coming from the paper.
One more in depth feeling that I recieve from Waterson is how alone Calvin is. Usually comics are not spent on a person who is constanly by himself, but this comic is different. Besides his parents and his stuffed tiger, there is only one or two other people ever in the strips. The rest is just Calvin using his imagination, or making observations.
This is why I still can appreciate Calvin and Hobbes as a comic strip. It's a shame that no more are made, but the ones that were will always hold a place on my bookshelf.