Anger is a complex emotion. Things would be easy if we could just say that being angry is always sinful. But that cannot be as the Bible records instances of God becoming angry (such as when the Israelites rebelled and made a golden calf). And when Paul urges us not to sin when we’re angry, the assumption is that it’s possible to indeed be angry without sinning.
I learned a lot about anger while reading Glittering Vices by Rebecca Konyndyk DeYoung. She points out how anger is actually connected to love as it can reveal what I really care about. 
Anger can also provide the motivation I need to make right something that is wrong. As Prof. DeYoung writes:
Anger, when it is a holy emotion, has justice as its object and love as its root. Both love and justice are focused on the good of others… Motivated by good anger, we hunger and thirst for righteousness, an appetite that depends on justice for its object, but on love for its right expression. Anger in these cases adds energy and passion to the execution of justice. The love that underlies it, however, keeps it in check, for love does not seek to destroy the other, but to set things right. (p. 130)
Vicious, sinful anger, on the other hand, Prof. DeYoung continues, is rooted in selfishness and harms others. Here’s my favorite line in her description of when this emotion gets misdirected:
Unhinged from justice, bad anger aims at another’s injury,
rather than another’s good. (p. 130)
Put less poetically, sinful anger causes more harm than good. How I need discernment to know when my anger is righteous and when it is making a hurt-filled situation worse!
Thinking about anger reminds me of this part of Psalm 103:
The LORD is merciful and gracious,
– – slow to anger and abounding in love.
God’s anger is perfect, yet He is slow to get angry. My anger is imperfect. I suspect it would most often be best if I were even slower to get angry than God!
(I’ve blogged about anger before.
It includes a classic Goofy cartoon!)
4th Point 