Re: the biggest difference
One user, padwinlearner, writes "in Islam, The Holy Creator of the Universe, man is trying to reach up to God through works (5 daily prayers, Haadj (spelling?), etc.). Christianity is based entirely on forgiveness, Islam is based on doing more right than wrong. The two views are diametrically opposed."
Padwin is right when he says that Islam is based on doing right. I think Padwin was trying to remember the five pillars which are declaration of belief, five daily prayers, giving aid to the poor, fasting, and Hajj (pilgrimage to Mecca). Yet even though these form the foundation of Islam, they are not wholly unique to Islam. That is to say, Christianity also attaches merit to belief, prayer, fasting, charity, even pilgrimage. In fact, much of the practice of medieval Christianity bears great resemblance to Islam. These early Christians prayed regularly for salvation. They fasted during Lent and at other times. Many gave a tithe, a tenth of their income, to the church. Christians, both ancient and modern, made pilgrimage to holy sites. The Canterbury Tales are a great example of Christians making a journey to visit a holy site.
Looking at the history of Christianity and its teachings, I cannot find a basis for the claim that Islam and Christianity are diametrically opposed. Forgiveness is certainly important to Christians. But Muslims too seek the forgiveness of their Lord because they know their deeds are imperfect. Muslims also acknowledge that it is by the mercy of the Creator that they enter heaven. Muslims do not expect to enter heaven without the forgiveness of their Creator.