As well as being a great historian Plutarch was a philosopher who used the examples of good and infamous men alike to reinforce his conception of morality and what the best in a man can truly be. Unlike other classical historians, he doesnt just accept stories about individuals at face value but always mentions conflicting facts in the historical record. He often digresses in mid narrative, but never to the readers frustration, as it is always with an eye to the social practices and political environment of the people of whom he writes, analyzing deeply with an anecdote here or an quotation there the merits and demerits of that society, and leaving us with a clearer picture of the classical mind-set as well as we might know it.
I can only say that as a classic of English prose style it ranks only second to Gibbon and reminds us that Plutarch means not just to educate, but to delight and entertain as well; such an achievement is not easily matched without the advantage of genius.