• God's anger is only good. He makes a just and justified response to true evils. At the same time, God is notably slow to anger and notably merciful (Exodus 34:6f); he does not treat us as our sins deserve (Psalm 103). But when God does express anger or warn of his anger, he expresses his goodness. “I will make my goodness pass before you and will proclaim before you my name ‘The Lord'” (Exodus 33:19). His character and name include his reckoning with evil.
• The devil's anger is only evil. It expresses his pride, lusts, frustration, cruelty, willfulness. He is always offended, always murderous.
• The willful, petty, entitled, irritable, argumentative, vindictive anger so typical of daily life is only evil.
• The anger of people toward genuine wrongs is usually mixed. Anger is a just and justified response to true evils, an expression of the image of God. The fact that we see a wrong as wrong is a good thing; the fact that we care enough to be troubled is a good thing. But human beings tend to return evil for evil, expressing the image of the evil one. For example, a person can get angry for good reasons, but express the anger in many wrong ways. The mix can be tipped significantly towards either end of the
spectrum. Sometimes it is barely good, quickly returning evil for evil. Sometimes it is significantly good in patiently and firmly facing down evil (though who of us is immune to the infiltration of self-righteousness?).
Read the whole article to see how he works out the false presupposition that anger is "morally neutral" and how anger is very much morally conditioned (either good or evil, but not neutral.)