Did a relevant philosophical background is necessary to consider a fiction as a good piece of literature?
Russian author's example for affirmative answer: Dostoevsky, his novels are full of existentialism interrogations judiciously incarnated by his characters.
Another Russian author's example for negative answer: Nabokov, his novels have an excellent style of prose and many appealing themes, but they are not particularly challenging on a philosophical level.
On the French side, it's kind of the same thing that differenciates Sarte from Celine, for example.
So, what's your opinion on that question?