What is good?

Some 2500 years ago, Socrates wondered about gods and goodness. In ancient Greece where he lived, many of the gods indulged in behavior which even mortals felt were bad, killing, stealing, commiting incest, destroying etc. He posed the question to Euthyphro about whether the gods love what is holy or holiness is what gods love. Socrates's student Plato wrote about. Today, this is known an Euthyphro's dilemma. Is God good because he conforms to a behavior that we all agree is good, or is good that which we attribute to what God does? If there is a good to which God has to conform in order to be good, then God is not the highest good and ought not to be called God in the first place. If good is what God does, then there is nothing that God does which is not good. In other words, is God good, or is good God?
Some say that this is a problem for Christians since if good is God, then God can be arbitrary and command evil which we have to define as good!
While this is a philosophical possibility, it assumes that goodness lies in the commands of God rather than in the nature of God. If god's nature is what we define goodness to be, then God's nature which determines God's commands, cannot be evil.