WHY IS GOD DIFFERENT FROM THE OLD TESTAMENT TO THE NEW TESTAMENT?

Many people ask this question especially in relation to understanding the line between God's mercy and His judgment.  It is much easier to look at God from the outside than from in the inside.  This is the issue.  In the OT God seems to be much angrier than He is in the NT.  Why is that?  We read incredible stories of judgment and destruction and see that as how God wanted to deal with people.  By taking a closer look at those stories and understanding the situations that were going on, you risk digging deeper into uncovering the truth.  From the surface like simply looking at the picture on a book cover, your assumption becomes fact in your mind.  By truly wanting to understand, you need to investigate.  If someone stole your identity, you would immediately stop everything else in your life that is going on to find the culprit and discover how it happened, RIGHT?  Be honest. Let's be real. No faking here.  Don't hide behind excuses and make an honest effort.  In every act of judgment God struck upon people, this action followed years of begging people to turn from their evil ways and from their evil gods along with their idols.  God was provoked by the wickedness and refutal of man.  Back then there were rebellious angels that came to the Earth and ruled over men becoming their kings.  They had sexual relations with women and begat the offspring of the Giant race.  Men simply became slaves, eventually.  In the NT, however, a prophesied well-kept secret of God's mercy gets unveiled.  Jesus Christ, God in the flesh, coming to redeem everything Satan took from Adam while creating a new and more excellent covenant with the Father. What are your thoughts on this?