I've read the book.. It won't matter if the original story is known, the two main characters are represented, but like the other review mentions, it is a loosely based re-telling of Robinson Crusoe.
The soundtrack which is entrancing, has me return to it, and keep looking for a copy, but the animation is also psychedelic, and thrusts a fantasy full of allegoric wonder in your face, and gives impression of what it must have been like in the late 60s/70s, if it was as hippie dippy as entertainment makes it seem.
This is for those interested in a pleasant, artsy pastime movie, and there's very few moments which would be depressing, with exception to a few which drive the story forward; one of the movies I'd leave on in the background for the ocean sounds.