I much remember this film from my teenage years. I am a real fan of both Ringo Starr and Harry Nilsson so to have both is a plus. The soundtrack alone is worth the time.
****SPOILER ALERT**** I won't tell the whole plot but if you want to experience it by yourself, look no further.
The film tracks Oblio and his dog, Arrow from the time of birth until his banishment to the Pointless Forrest. He learns many lessons while traveling from the denizens of the Forrest. He and Arrow return, teaching those that banished him important life lessons he had learned.
The animation is not as sophisticated as The Yellow Submarine, but it is treasured by me just as much.
What's great about it: Teaches about racism and the consequences through music.
What's not so great: Simplistic for adults, probably.