I can’t say that I have liked Calvin and Hobbes since my childhood, heck I only discovered Calvin and Hobbes about 5 years ago. But from then on I was hooked. The moments of the (relatively) carefree life of Calvin intertwined with subtle philosophical questions or observations on the world grabbed my attention (and that of many others). It somehow gives you everything you need: the imagination to make even the most boring moments exciting, a dad that makes up explanations for the physical world that make absolutely no sense, sleigh rides, the sense of humour of a six year old (zombie snowmen) and of course a plush toy that is also his best friend.
Bill Waterson, the creator of Calvin and Hobbes never anticipated having such a success with this newspaper comic and is unsure why his cartoons have been so successful. And after 10 years Bill Waterson stopped with Calvin and Hobbes.
Bill Waterson never allowed the production of merchandise or to continue on with the cartoon. And I think this is why it is still such a popular cartoon. It feels like the cartoon stayed true to the nature of the characters.