In my book, the problem is that the entity that spoke to Mohammed, was not God. 'Twas Satan who whispered his lies to that fool, calling himself God. Mohammed was but a useful idiot in a larger scheme.
Muslims believe that Allah is God but that is false. The god of Islam is not "the personage we refer to in English as 'God'."
Just my personal opinion.
A Christian handbook for converting Arabs has been discovered in the text of the Koran ~ it's in Aramaic.