The Cruel God of the Old Testament?

Many believe that God the Father is cruel and harsh, but Jesus Christ is the merciful and the loving Son of God who must intrigue the Father on our behalf so that He is less angry with us. This belief is based on the idea that the Father was the angry God of the Old Testament who did terrible things to the people, while Christ, the innocent Lamb, is our loving Mediator to beg the Father to show love to us. Why are these ideas totally wrong? And what DOES the Bible say about God’s love and punishment?