Herman Hesse is my Tesla, my Einstein, my guru. I first read "Siddhartha" quite young, and by my early teens I'd read both "The Glass Bead Game" and "Magister Ludi" - a different translation a bit harder to read - I'd read them both multiple times.
Hesse's philosophy is so comprehensive, there is no trite summary. Perhaps simply viewing life as a series of symphonic movements, with competing harmonies and melodies is as short as one can get.
The closest I can get to describing his philosophy is that he is focused on the tension between book learning and experiential learning (particularly as manifest in the outdoors). The other theme that comes up repeatedly is the relationship between students and teachers (both those that are in the official role of teacher, and more often those that are teachers because a student, often the protagonist, chooses to follow them and learn from them).
He is great. Also try existentialist literary fiction. Russian writers do an amazing job by designing rich characters and writing good conversations which will resonate with you if you like Herman Hesse's work.
Hesse's philosophy is so comprehensive, there is no trite summary. Perhaps simply viewing life as a series of symphonic movements, with competing harmonies and melodies is as short as one can get.