The role is usually both political and dramatic; with the malcontent voicing dissatisfaction with the usually 'Machiavellian' political atmosphere and often using asides to build up a kind of self-consciousness and awareness of the text itself which other characters in the play will lack to the same extent.
The morality and sympathy of the malcontent is a massive variable, as we can see in the examples listed above. Sometimes, as in 'Hamlet' and 'The Malcontent', they are the sympathetic centre of the play, whereas Iago is a very unsympathetic character.
The most important thing about the malcontent, is that he is malcontent—unhappy, unsettled, displeased with the world as he sees it—not at ease with the world of the play in which he finds himself, eager to change it somehow, or to dispute with it. He is an objective or quasi-objective voice that comments on the concerns of the play and comments as though he is somehow above or beyond them.