No, the OT and the NT God are not two sides of the same coin. God is just as much a perfectly righteous being who is a judge as he is a merciful God who rescued us through his Son, Jesus. We must all meet God’s perfect standard to escape his wrath...unless we realize we’re sinners, repent, and take the way out that Jesus provided. God is a God of great wrath...He is also a God of great mercy and He provided a way out of the path of His wrath for us.
Yahweh, with his flood that killed millions who displeased him, was wrath incarnate. Don’t see much of that in the NT.