Good books can be for both young and adult reading.
One thing I’ve been reminded of through reading (and enjoying) the Harry Potter books is that just because a book may be written with a young audience in mind doesn’t mean it’s not a good adult read.
Modern-day authors like Pullman and Paolini have written some hefty-sized ‘teenage’ books which I’ve found quite captivating. The Narnia series by C. S. Lewis seemed to me, when reading them during my childhood, as a good, fun, adventure story involving the fight of good and evil. However recently reading them again as an adult, although not a particularly intellectually demanding read, the interplay of the various characters can take on a far greater meaning when viewed from an adult perspective. (Now I think about it, I really must read Lewis Carroll’s Alice’s Adventures in Wonderland again.)
Eoin Colfer’s Artmis Fowl books have always entertained me, though I do think his latest in the series, The Atlantis Complex, a little bit weak. I’ve also enjoyed following the adventures of Howl and his Moving Castle. (Diana Wynne Jones.) Another favourite has been the Mortal Engines series by Philip Reeve.
I suppose it all depends what you want from a book. Sometimes it’s nice to have something that taxes the brain and is a demanding or challenging read. Something that really makes you work and in turn can provide a tremendously rewarding reading experience.
Other times though, it is nice to be able to relax and allow yourself to flow into the story without too much effort, where it’s easy to allow ones imagination to head off into another world. Life without this bit of escapism would be a so much more stressful place.