"Meno" is a great work because it challenges the reader to question his definitions of certain concepts in order that the reader may seek to find what that concept really is. Meno thinks he knows what virtue is and defines it as being different for each type of person; for instance, virtue for a man is governing his affairs well while virtue for a woman is being a good housewife and being obedient to her husband. Socrates then asks Meno questions such as what do all virtues have in common that make them virtues. By questioning Meno thus, he is forcing him to clarify what his idea of virtue is. This is crucial, for one cannot act virtuously if one does not know what virtue is. In this way, "Meno" challenges us to question not just our definition of virtue but all our ideas in order that we may be acting in accordance with reality rather than just an appearance that is actually far removed from reality.
I hesitate to quantify my evaluation of the book but since I must, I give it four stars because the dialogue seemed to stray from reason in certain points and turn towards the mystical. For instance, Socrates claims that knowledge is a process of recollecting knowledge from previous lives and thus it is accorded to one by divine dispensation. I think Socrates' method of questioning a person to elicit his beliefs is correct, but I do not think that his beliefs are elicited because they already present in his soul, but rather that they are arrived at through mental deliberation.
Many modern philosophers have debated exactly what "virtue" is, and how one becomes or is virtuous. Protagoras and Socrates, two ancient Greek philosophers actively debate this issue in this book. A warning: THE TEXT IS VERY CONFUSING, AND WILL PROBABLY HAVE TO BE READ MORE THAN ONCE. If you don't dig philosophy, I recommend you avoid this book, as reading it will give you a big headache. But for those out there who love philosophy, this book is definitely for you. I gave this book an 8 because it does an excellent job of explaining two different views on this subject, and will obviously attract philosophy buffs.