I enjoyed his book on Socrates, however people should Be the wary of Kreefts beliefs. His book, Ecumenical Jihad, advocates Christians and Muslims coming together and in spiritual unity to rid the world of evil and atheism.
If I remember correctly, the book on Islam has a copyright of 2001 or something like that. It certainly was written before 11 Sept. I think his views have moderated somewhat. I am pretty sure he is reluctant to advocate violence.
He is rational and I do not have a problem with his views on Islam even if I think he may be wrong. His views are not unrealistic. The vast majority of Muslims I have known do not fit the image imparted on this site though I had a student from Palestine who was way whacked out. Every paper he wrote was about killing Jews. Yes, I told my supervisors. Fortunately he was so stoned all the time he lacked the will to do anything.