Not scary, but a FANTASTIC read with "adult" philosophical concepts is "The Chronicles of Hawklan" by Roger Taylor. The books in the initial series are:
"The Call of the Sword"
"The Fall of Fyorlund"
"The Waking of Orthlund"
"Into Narsindal"
I was really, really surprised when I first read these and now read them again at least once a year.
Scary fantasy: "Mulengro" by Charles de Lint. He is one of my favourite Speculative Fantasy authors and most of his books have a kind of scary element to them as well.
Hope this helps
Blessings!
Duskwynd