Old Testament Queries...

Ever heard the story from the Old Testament when Isaac took his only son to be killed to show his devotion to God? After hearing this today, I realize that the God of the Old Testament is a cruel and often ruthless. How is this the same omni - benevolent God that Christians read about in the New Testament? What kind and loving creator would demand of a man his one and greatest joy to simply show devotion to him? I thought that Christians, like many other religions, show devotion to God in their everyday actions and prayers. Is this not good enough? The Bible is ambiguous at times...