Because God created the Son, the angels, Man, Heaven, Earth, and everything else, and since he is omniscient, Milton was faced with the difficulty of creating tension about what would happen since God already knew. This problem, of course, existed in one way or another in most Greek epics and tragedies so that the real question was in the presentation of a known set of incidents. Milton approaches the problem of God's character by making him almost a chorus-like figure. God comments on scenes and actions, he explains what will happen and why, he gives the philosophical / theological basis for ideas like free will, but he does not truly participate in the action.
God is aloof, almost emotionless. He embodies pure reason, and consequently his responses often seem cold. In the war in Heaven, God limits the power of the faithful angels and in the final moments sends only the Son to conquer the rebels. Yet his cosmic laugh at the presumption of Satan and his crew has a chilling effect. If the reader had had any doubts about Satan's power against God, that laugh puts them to rest.
God's unemotional reason is not without another side. God is also pure justice. He may see his plans for Man dashed by Satan's trickery, but through divine justice, he will put everything to right and conquer Satan. From evil, God will produce goodness. God gave Man free will. From Man's free will, sin and death came into the world, but God will see that goodness rules in the end.