How does the reader reaction to Brutus's death in Julius Caesar?

Brutus killed himself when Antony and Octavius’s armies were moving in on him.

Brutus died an honorable death, by Roman standards.  Rather than allow himself to be captured, he killed himself.  Suicide was considered a noble alternative to being paraded through Rome in a triumph.  When all seemed lost, Brutus took his life. 

Antony makes very celebratory comments about Brutus when they find his body.

This was the noblest Roman of them all:All the...

Brutus killed himself when Antony and Octavius’s armies were moving in on him.

Brutus died an honorable death, by Roman standards.  Rather than allow himself to be captured, he killed himself.  Suicide was considered a noble alternative to being paraded through Rome in a triumph.  When all seemed lost, Brutus took his life. 

Antony makes very celebratory comments about Brutus when they find his body.

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 in him that Nature might stand up
And say to all the world 'This was a man!' (Act 5, Scene 5)

Why did Antony consider Brutus so noble?  Unlike some of the other conspirators, Brutus did what he did for the good of Rome.  He did not desire power or wealth.  He was already an important senator and from a rich family.  There was nothing ambitious about Brutus.  He took part in the conspiracy to kill Caesar because he thought that Caesar was a tyrant.

Brutus often acted foolishly, it is true.  He was naïve about how the people would react to the conspirators’ actions.  He cared more about image than about fact.

Let us be sacrificers, but not butchers, Caius.
We all stand up against the spirit of Caesar;
And in the spirit of men there is no blood:
O, that we then could come by Caesar's spirit,
And not dismember Caesar! But, alas,
Caesar must bleed for it! And, gentle friends,
Let's kill him boldly, but not wrathfully … (Act 2, Scene 1)

Brutus made some bad decisions, including allowing Antony to speak at Caesar’s funeral instead of killing him like he probably should have.  Taking their armies to Philippi was also a bad idea.  He should have listened to Cassius, who had more experience.  However, Brutus believed that his cause was the right one.  He died doing what he thought was honorable.