The God of Islam is described as not having a nature. By this I mean that he does as he wishes without any seeming logical system for making those decisions.
The Judeo-Christial God is seen as having a very definite and unchanging nature.
Allow me to illustrate. There has been asked the question "Can God make a rock so heavy, he can't pick it up?". In Islam I would argue the answer would be no. Being all powerful, but without an unchaning nature, his will is whatever it is at that moment. The God of Abraham in theory could make a rock so heavy he couldn't move it. In a sense his nature is unchanging, therefore he cannot do anything that is aginst that nature. After the flood of Noah, God promised He would never again destroy the earth in such a manner. Is he physically able to do it? Yes, but he will and cannot because it is not in his nature to lie.
Another difference in Islam and Christianity is their views of spreading their religion. Christianity places the emphasis on the resposibility of the individual to choose to believe. The message is to be preached, but each person must respond on their own. In contrast, Islam teaches that the world must be conquered by Islam. This is why, I believe, there are so many Islamic theocracies. A person is resposible for choosing Islam, but they do not have a choice in rejecting it. The non-muslim world is to be dominated.
Thirdly, Islam and Christianity differ in their idea if "heaven". The Islamic idea of heaven can be interpreted as being a sexual paradise. Dying and being rewarded with virgins. The Christian in heaven is "married" to Christ and will only serve him.
