Like many modern day critics of Scripture, Marcion of Sinope (2nd Century) understood and accepted the fact that there are irreconcilable differences between the way that God is portrayed in the two Testaments of the Christian Canon. What was his conclusion and solution? They can't be the same personage, so Christians must reject their Jewish roots and the Old Testament!
In similar fashion, many folks in our day have decided to walk away from both Testaments. They reject the attempts of Fundamentalists to reconcile the differences as feeble, disingenuous and illogical. After all, their apologetics are based on the premise that Scripture cannot contradict itself (a thesis that engenders a lot of circular reasoning).
Nevertheless, in fairness to the founder of Christianity (Jesus of Nazareth), I think it should be noted that he didn't attempt to justify the Old Testament depictions of God or reconcile them to his own portrayal of the Divine. In fact, he underscored the contrast!
Jesus said that God was NEVER for divorce (he said that was a Mosaic invention to accommodate their hard-heartedness). He said that God didn't sanction revenge - that "an eye for an eye" wasn't God's principle. He taught that his Father wasn't legalistic about Sabbath observance and didn't countenance using religion or devotion to himself as a justification for mistreating others. Jesus Christ taught that God was the embodiment of love, and that "He" wanted to save everyone (not zap or destroy them). Jesus said that God didn't just want us to abstain from murdering each other, but that "He" wanted us to refrain from entertaining feelings of anger and hatred for each other! In fact, one of the chief disappointments of both his supporters and detractors was his refusal to launch an Old Testament style genocidal war of liberation from the Romans.
In short, Jesus knew what many of us have come to understand: The human authors of the Old Testament had often attributed characteristics and feelings to God that did not belong to "Him." Christ was the antidote to those false depictions. He was meant to offer a glimpse into the TRUE nature of God. Jesus wasn't interested in reconciling the two depictions of God - he simply wanted to set the record straight. Notice also that he accomplished this without discrediting or discounting Scripture or rejecting the people and religious tradition into which he was born. In effect, his message was "you've got the right God, but your understanding of 'Him' and 'His' expectations is FLAWED!"
From my perspective, that's a much more satisfying approach to the problem than the apologetics of the Fundamentalists or the rejection of a Marcion or Dawkins. What do you think?