As a child I loved the Lorax for the simple rhymes and laughed at the comical little Lorax standing up to the might of the Once-ler. I think from the standpoint that it is fun and interesting ryhme ranks it right up around the four stars mark because it got young children to read.
As an adult, I find the stance that the Lorax make for accountability to be a valuable lesson that adults can relate to children in explaining this story.
What I really like and thought it was well conveyed (despite the very dated background music and the liberal rewording to extend the poem) is that final stanza where Dr. Suess, through the Once-ler, lets us know that even with all the problems there is still a chance to better the world we live in but it will require great care and effort...