Lewis Carroll's novels are over 100 years old. Close to 150 years old. Not only have they not ever slipped out of the canon of "classic literature", they have had (as JCamilo pointed out) a clear impact or influence on writers ranging from other books written for children such as
The Wizard of Oz, C.S. Lewis'
Narnia, Neil Gaiman's
Coraline, and J.M. Barrie's
Peter Pan; to science-fiction such as Philip José Farmer's
Riverworld series; on through serious literature by writers such as James Joyce, Christian Morgenstern, Paul Auster, J.L. Borges, Vladimir Nabokov, etc... There are also quite literally hundreds of adaptions, parodies, or works influenced/inspired by the Lewis Carroll novels to be found in comic books, animations, film, television, theatrical productions, erotica and pornography, video games, painting, sculpture, pop music (the Jefferson Airplane's
White Rabbit and the Beatles'
Lucy in the Sky with Diamonds and
I am the Walrus to name just a few), music videos, and even opera. When there is this kind of interest and influence 150 years after the fact... after the PR machinery and the marketing and the fads have all dissipated... there is more than a good chance that what you are looking at is a "classic" whether you personally like the work or not. - Stlukesguild