It is a testimony of the nobility of Brutus that his arch-enemy, Marc Antony, praises him at the end of the play in his eulogy,
This was the noblest Roman of them all:
All the conspirators, save only he
Did that they did in envy of great Caesar,
He, only in a general honest thought
And common good to all, made one of them.
His life was gentle, and the elements
So mix'd him that Nature might stand up
And say to all the world: "This was a man!"
That Brutus has "general honest thought" and is virtuous is evinced in his decision to slay Caesar whom he considers a threat to his beloved Rome in the early part of the play, in his speech to his loyal wife Portia, and even in his treatment of his friend Cassius. For, in Act IV, Scene 3, when Cassius urges Brutus to defend his friend Pella, Brutus ignores the letters of Cassius, allowing Pella to be rightly punished for taking bribes. Later he chides Cassius for his wrongdoing. He also continues to defend his belief in this argument that the assassination was a noble deed; this defense in light of the damaging civil war points to Brutus's self-deceptive commitment to principle.
In this argument with Cassius, Brutus also demonstrates that he is not perfect as he speaks rather rashly and loses his temper. Later, he does not listen to Cassius about keeping the troops where they are and letting the troops of the triumvirate come to them. Instead, Brutus orders the troops to Philippi, exhausting them before their battle, thus causing their defeat. This act of hamartis, in which Brutus feels
There is a tide in the affairs of men
Which taken at the flood leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures.(4.3.243-250)
is what causes Brutus's death. A noble Roman, Brutus is loved by Cassius, who is ready to kill himself after their argument in Act IV. Certainly, his misfortune is not entirely deserved; however, much like Caesar who exhibits inconsistencies before he goes to the Senate, Brutus, too, is inconsistent, discounting fate earlier then calling for the moment to act in his "tide in the affairs of man" speech. And, tragically, Brutus is too much of an idealist. It is he who is the tragic hero of Shakespeare's play.