(It took me three tries to get past the first tangental monologue chapter, and I was deeply rewarded by doing so. It's a great book but not what you may expect based on the title or first chapters)
If someone offered me one million dollars to clearly explain the book to them right now, I wouldn’t be able to do it.
To take a stab at it:
On the top layer it is a mostly true story about a man, his boy, and a couple of friends taking a motorcycle road trip from Minneapolis to San Francisco.
The next layer is significant portions of the book which the author calls a chautauqua which was a thing somewhere at the intersection of TED talks, a variety show, and a university lecture. He goes on about Zen, motorcycles, and philosophy partially through recollections of his own history (spoiler alert: unreliable narrator). The central theme is his own definition of Quality used as a bridge between exacting analytical logic, "western thought" and emotional, subjective, artistic, "eastern thought", and beauty.
On the third layer, you get to watch the author, who experienced significant mental health issues (I think schizophrenia) and electroshock (not positive this part was true) who sort of came over the hill into a more healthy mind but still experiencing some megalomania writing a somewhat grandiose book about his own history and thoughts, his relationship with his son, and growth.
But yeah I drifted through a number of the monologues with a determination to make it through to the end, not easy at parts.
Easier than Godel Escher Bach however! Pretty sure I'll never get through that one