Spengler has a fascinating essay on why Islam is more akin to paganism. The essential difference? Free will. Which Jews and Christians both believe has been given them by our creator. Free will, along with an ordered universe created by God, requires us to reason; requires rationality.
This is a stark contrast with Islam, where the reigning philosophy is “Whatever Allah wills,” as expressed with the typical “Insha’Allah.” Since Allah as conceived in Islam is a totally transcendent being, and since he is directly running everything all of the time, why strain ourselves with an attempt at rational thought?
From Spengler, more on the essential distinctions between God and Allah:
The Judeo-Christian God loves his creatures and as an act of love makes them free. Humankind only can be free if nature is rational, that is, if God places self-appointed limits on his own sphere of action. In a world ordered by natural law, humankind through its faculty of reason can learn these laws and act freely. In the alternative case, the absolute freedom of Allah crowds out all human freedom of action, leaving nothing but the tyranny of caprice and fate.
Remember the totally different conceptions of God the next time some apologist for Islam tells you that “Allah is only the Arabic word for ‘God.'” True in the literal sense. But Islam has a far different concept of God; a concept that is in grave error and which explains much about the Islamic world’s intellectual stagnation.