Palmer, John. "Marcus Brutus."
Political and Comic Characters of Shakespeare. London: MacMillan, 1964. 1-64.

Thesis: Palmer, a vigorous stylist, opens his essay briskly:
Brutus has precisely the qualities which in every age have rendered the conscientious liberal ineffectual in public life. His convictions required him to take the lead in a political conspiracy which, for its success, called for great agility of mind, a deft and callous adjustment of means to ends, acceptance of the brutal consequences which attend an act of violence, and insight into the motives of men less scrupulous and disinterested than himself. In all these respects he was deficient. Brutus, plotting the assassination of Caesar, did violence to his character, entered into association with men whom he did not understand and involved himself in events which he was unable to control. He committed himself to a course of action which could only be justified by principles which had ceased to be valid for the society in which he lived which entangled him in unforeseen consequences with which he was unable to cope.  (1)
After this introduction, Palmer proceeds with an analysis of the characteristics of Brutus that we see in his first appearance; he is a "recluse," "divided against himself," recoils from action, has difficulty concealing his thoughts, is a devoted republican, but a "reluctant conspirator" (1-3). Then, delving ever deeper into Brutus' character, Palmer compares him to others in the play. The realism of Cassius contrasts sharply with "the confused thinking of Brutus and its sharp divorce from political reality" (6); "Brutus, the recluse, despises Antony," but "it is just because Antony is a sociable person that he can so effectively adapt himself to all occasions" (17). Palmer also examines all of the scenes in which Brutus plays a significant part, always with an eye to detail, as in the following description of the moments before Caesar's ghost appears to Brutus:
Observe the exquisite courtesy with which he bids Varro and Claudius lie down in his tent; his tender concern for the boy Lucius, nodding over his instrument; his apology to Lucius for asking him to play and for having accused him of mislaying the book which he had forgetfully slipped into his pocket—the book itself 'turned down where I left reading'. Note especially how these touches, which endear Brutus to our hearts, continue to mark him as unfitted for the part he has been called upon to play.  (60-61)

Bottom Line: Everything you might want to know about Brutus.