Hard one to answer. As you get older books don't smack you as hard, and the profundity just isn't there no matter who you read. Nowadays I find that I don't get the "holy shit, this guy/gal is a genius!" kind of reactions to books anymore, and my appraisal will suffer for it.
For instance, I read The Picture of Dorian Gray as a youngster and thought it was amazing. Even tried to rationalize some of it by suggesting that the thoughts we conceive come to transform our features because we are exercising (or not exercising) certain of our facial muscles, making them prominent (or not) - so if we smile a lot the muscles employed in smiling will become prominent and we'll look like a "happy person", and if we scowl alot... you get the picture.
But when I reread it in later years - it might be the only book I've ever reread - it didn't seem that great. Great writing, but the ideas didn't seem especially intriguing and for me it's all about the ideas.
I will say that I like Russian authors - the plot always seems to take a back seat to the characters, and man can they paint a portrait. Dostoyevski and Tolstoy don't really seem to give a shit about what happens, they only care about how people react to what happens, and for some reason that seems realistic - in real life, for the most part, nothing fantastic really happens to the average person, but the little things that happen still provoke great reactions nonetheless, and these are the sustenance of our daily interest, so reading of the same rings true for me.
Probably Hermann Hesse though: Naricuss and Goldmund. Deeply resonant.