Literature: Character, Style, Tone and Language

Is "Roses are red/ Violets are blue/ Sugar is sweet/ And so are you!" poetry? Why -- or why not? What, in other words, makes a group of words a "poem"? Is there a difference between "poetry" and "verse"? If so, what do you think it is? Along with your response, please list a poem, along with its poet, that you find particularly well done, and share it with the class. Please explain why you chose it.