I think I am curiously resistant to books that have been telegraphed to me as "deep." Some small part of me digs in my heels and says "oh yeah?"
Siddhartha would fall into this category. It's a fairly simple parable, fairly straightforward in its Western exploration of Eastern religion. It was a fast read....
I don't, though, feel like it changed me or will stick with me. I already knew everything about Eastern religion that Siddhartha tried to express. (This is not to say I am particularly well versed in Buddhism or Hinduism, but enough so as to have already heard this all before.) Also, when your main character says enlightenment can't be taught or explained, but then the book is trying to show how he achieved it, isn't that contradictory?
As far as star ratings goes, this could maybe be a four. Maybe. It was a quick read, a painless one, but didn't strike me deeply.
Some books just leave me feeling like I didn't get it. This is one of them.