Trying to describe what God is difficult because He is so great that it is hard to know where to start!
A great man named Moses asked God to show Himself to Moses. God gave this description of Himself:
The LORD passed by before him and proclaimed: "The LORD, the LORD, the compassionate and gracious God, slow to anger, and abounding in loyal love and faithfulness, keeping loyal love for thousands, forgiving iniquity and transgression and sin. But he by no means leaves the guilty unpunished, responding to the transgression of fathers by dealing with children and children's children, to the third and fourth generation."
(Exodus 34:6-7 NET)