An Old Testament God?

I was preparing for our study of Islam, which I'll be leading tomorrow.  We're using Adam Hamilton's Christianity and World Religions (Abingdon) as our foundation (has video and leaders guide).  My point is not to talk about the series, but to raise a point (Hamilton is a centrist United Methodist in theology).

Hamilton does something -- something I hear Christians do fairly regularly -- and that is distinguish between the God of the Old Testament and the God of the New Testament (of Jesus).  In his discussion of Islam, which is really quite fair when it focuses on the teachings of Islam, he suggests that the Muslim view of God is a step backward toward the God of the Old Testament.  That is, the Old Testament portrayal of God is one that, unlike the NT, is more violent and less loving.  He uses God's command to Elijah to slaughter the priests of Baal.  Jesus doesn't do this (though Hamilton and many other Christians forget about what happens in the Book of Revelation). 

The problem here is one that has plagued Christians almost from the beginning.  We want to see ourselves improving upon Judaism.  We may not go as far as Marcion, who suggested that the Creator God was a "demiurge," a lesser God than the God of Jesus, who is the God of love.  Marcion went so far as to create a truncated canon of Scripture that would support his claims.  

But what are we who are Christians saying when we say that the God of the OT is a more violent God than the God of the NT?  Obviously there is doctrinal development in the OT and the NT.  Both testaments come out of particular contexts, but is the Christian understanding of God better than that of Judaism?  And is Muhammad's view a step backward to a Jewish view?   Or, would it not be best to say that all three religions give different perspectives on God, some more violent and some more peaceful? 

I end with this word from Disciple theologian Clark Williamson:

In their post-Shoah teaching documents, the churches affirm that the God whom Christians worship is the living God of the Bible, the God of Israel, worshiped by Jews.  They assert that Christians have come and still come to know this God in Jesus Christ -- that in, through, and by means of Jesus Christ Christians are again and again confronted with the promise and command of the God of Israel.  That the God of Israel was incarnate in Jesus Christ, the Jew from Nazareth, is a claim that further makes it clear that the God of Israel "is not an isolated God without relationships, but a God who turns toward humankind and who is affected by human destiny."  God, who dwells not only in transcendence but in the midst of God's people is subject to distress and persecution "as Lord, Father, Companion and Redeemer." The covenantally related God of Israel, whose covenant love (hesed) involves God in interacting with all God's creatures and particularly with God's people, is here asserted against the church's tradition of construing God as in all respects unrelated to and unaffected by events in the world.  (Williamson, A Guest in the House of Israel, p. 202)

The quote is to a German Roman Catholic document from 1979.  Clark Williamson asserts that the God of Jesus is the God of Israel?  If Jesus is understood as the incarnation of that God revealed in our Old Testament, how can we make such a distinction between the God of the OT and the God of the NT?