The prime mover of the Beatles wrote this and that is why it's still in print. It has its interesting points outside of the fact that it's John writing it: The wordplay is fun, the drawings are amusingly silly and Paul McCartney did a mirthful little preface.
But, if you're looking for the lilting poetry you hear in such songs as "A Day In The Life," "Across The Universe," "Imagine" or "Number 9 Dream," you're not going to find it here. John Lennon was a great songwriter whose lyrics matched his plaintive melodies. The little items in IN HIS OWN WRITE are the fun little things a genius does when he's not doing what he really loves to do.
An anecdote: In 1973, when I was a spending all my waking hours hoping for a Beatles reunion, I noticed a first edition of this in a little memorabilia shop in my town. They wanted ten cents. I had forty cents. The bus home was thirty-five cents. I paced back and forth, missed the bus, paced back and forth again and then went outside, without buying the book and got the next bus. I have been kicking myself for thirty-four years now!