For most critics, Viola is one of Shakespeare's most delightful and beloved feminine creations from his comedies. Surrounded by characters who express the extremes of emotionalism and melancholy — that is, Viola is caught between Duke Orsino's extreme melancholy and Lady Olivia's aggressive emotionalism — yet she represents the norm of behavior in this strange world of Illyria.
Due to her circumstances, she is, first of all, a very practical and resourceful person. As a shipwrecked orphan who has no one to protect her, she must resort to some means whereby her safety is assured. She knows that a single woman unattended in a foreign land would be in an extremely dangerous position. Consequently, she evaluates the sea captain's character, finds it suitable, and wisely places her trust in him; then she disguises herself as a boy so that she will be safe and have a man's freedom to move about without protection. Consequently, Viola is immediately seen to be quick-witted enough to evaluate her situation, of sound enough judgment to recognize the captain's integrity, resourceful enough to conceive of the disguise, and practical enough to carry out this design.
Viola also has a native intelligence, an engaging wit, and an immense amount of charm. These qualities will help her obtain her position with Duke Orsino, and they are also the same qualities which cause Lady Olivia to immediately fall in love with her. It was her charming personality, we should remember, which won her the sea captain's loyalty, without whose help her disguise would have never succeeded. And within a short three days' time, her wit, charm, loyalty, and her skill in music and conversation won for her the complete trust of Duke Orsino. We should also remember that even though she is in love with the duke, she is loyal in her missions when she tries to win Lady Olivia's love for him.
For the modern audience, Viola's charm lies in her simple, straightforward, good-humored personality. She could have used her disguise for all sorts of connivings, yet she is forthright and honest in all of her dealings with Lady Olivia and with Duke Orsino, albeit she does use her disguise to entertain the audience with delightful verbal puns. Perhaps the most surprising thing about Viola is that a young lady in possession of so many attributes falls in love with someone who is as moody and changeable as the duke.