I had a period I read only one writer at a time; Poe, Lord Dunsany, Lovecraft, Howard, Clark Ashton Smith, Arthur Machen roughly in that order, and in my younger days I read nearly everything Moorcock had written. But it's easy to get over satiated that way (especially on Lovecraft), and I enjoy a more varied diet now.
Totally ... variety and spacing out similar elements is everything I reckon. Many years ago, I burnt out on Fantasy, during a period where I was laid up for several months, and that taught me to read more wisely, so I could get the best out of every read.
If I had time I would read mysteries too, especially Christie. So much too read, so much to play, so little time. I don't understand kids when they say "I'm bored".
I don't understand it either, but getting started is no doubt the hard bit. My two adult youngest suffer from that I think ... but then they have so many other distractions these days that are easier to get into ... games for my youngest lad and movies/TV series for my daughter. My youngest lad has been stuck on the second Witcher book for about a year now. My oldest lad reads a lot of non-fiction, far more than me.
BTW, you sound quite well read. Surprised you can get into Feist and Pratchett. I found Feist's "Magician" too juvenile when I reread it about 5-10 years ago.
Mmmm sorry, can't agree with you there ... must be a perception thing or something.
My all time favorite author is Terry Pratchett, his mind is second to none ... a very smart and perceptive man. He can take a while to appreciate, but once you get it and that style of English humor, it is brilliant. I never used to be into what I initially saw as a parody of fantasy by Terry Pratchett. I almost gave up on him after reading the first Disc World novel, but I kept going, because I wanted to read Mort, which was about 4th in the series. By about the third book I was hooked and starting to appreciate the depth of where the author was coming from. Many of his later books absolutely blew me away ... a very clever and deep man, who knew humanity well. Not surprising that he was King while J.K. Rowling was Queen.
Dan Brown is probably my second favorite author, but I have many favorites. He likewise has an amazing mind.
And I have read The Magician by Raymond E. Feist twice ... second time was the extended version, and I loved it each time. In fact, Raymond along with Janny Wurts has written (co-authored) my all time favorite story, their Empire Trilogy ... a very complex and multi-layered marvel, with a nod to many genres.
Personally I only consider something juvenile if I find the author is writing down to you, like you are a simple child, when they shouldn't be ... so it's insulting ... treats you like an imbecile really.
Hell, the most important series for me that I still love, which had a big impact on me, and still effects me emotionally to this day, is the Narnia series by C.S. Lewis. Written for children I know, and full of allegory which upsets some ... I'm not religious either. However I still feel the glorious magic and wonder over five decades later ... re-read it many times, and to each of my three kids as they were starting out with their more adultish type reading. I was 7 or 8 when I read The Lion, The Witch And The Wardrobe with my dad ... finished the second half on my own.
Narnia stories, while written for children, never felt like they were written down to a simpleton, and they always felt like the author was cognizant that adults would also be reading them. Still, it is often about perception and I know many find them childish ... sad really. I've never lost touch with my inner child, and feel sorry for those who have.
To be perfectly honest, I don't like a lot of juvenile books written for children. But I do love ones that acknowledge how bright children can be. David Walliams for instance writes brilliantly. Dr. Seuss is another. Clearly I also like the humor side of things. A good children's book to me, is still a good adult book ... it just misses concepts that might be difficult for children to understand or relate to. A good adult book doesn't have to contain all the things that many do (i.e. sex and violence) ... and I say that as someone who loves the writings of Val McDermid, J. Robert Kennedy, C.J. Box and others, which can be very dark psychological thrillers.
I read to learn and or be entertained. I like to have my concepts or ideas challenged, but don't like it when things get too preachy. Terry Goodkind is a brilliant writer, but he can get too preachy sometimes. Same for Piers Anthony, though in a different way. Stories that make me think are great, but so are ones that are just nice easy reads. I love complexity too, to a point ... I am a complex simple man after all ... or is that a simple complex man ... I can never quite tell or remember. ;)
P.S. It is my personal view, that many over-analyze stories. They make it too clinical. Reading should be a joy I reckon, a journey to elsewhere, an escape when needed ... or not ... nourishing and maybe enlightening. Sometimes it is important to suspend disbelief to get to what really matters.