Alignment in D&D has always been something that is criticized, caused countless arguments, and seemed completely arbitrary. For the past several years I have used my own version of alignment. I have still been using the standard labels of Lawful, Neutral, and Chaotic from Classic D&D, but with different meanings. In my games alignment is more of a general philosophy or mindset of the character; alignment represents how the character views the world. Someone who is Lawful beleives that government and Laws are good and that man needs government to be good; while a chaotic person believes that man is naturally good and that society and government corrupt the soul. It is basically the argument between the the philosophies of John Locke and Thomas Hobbes. Neutral would be someone who has a middle ground philosophy or doesn't care/hasn't put much though into it.
Despite sticking to alignment for so long, I'm finally going to abandon it. I am thinking of using religion instead to guide how NPCs will react to characters and as basis for the clerical class. As argued on Grognardia and Delta's D&D Hotspot Clerics in the original game belonged to a monotheistic/christian faith. There was an implicit presence of an underlying politically powerful and christian based religion in the early games of D&D run by Gygax and Arneson. Also, if I am using the Known World setting, the Empire of Thyatis is described as having a Byzantine culture. How can I have a Byzantine culture without Christianity? The Church was an intrinsic part of the culture of the medieval byzantine empire, not to mention the other countries of the known world based on medieval Europe.
The Known World won't be drastically different due to this change, simply many of the churches will be monotheistic instead of Polytheistic. Religions/ Churches of different regions are as follows. Thyatis, Karameikos, Corunglain, Minrothad, Darokin, Ostland = monotheistic(Christian). Atruaghin, Akesoli, Akorros, Ierendi, Selenica, Ylaruam = monotheistic (Islamic). Glantri = polytheism (Druidic). Ethengar = Shamanism. Sind = polytheism (Hindu). Heldann, Vestland, Soderfjord = polytheism (Norse). Malpheggi Swamp = polytheism (Egyptian). In the future I will go into more detail about the dominant church in each region and the class associated with each faith. Basically the traditional cleric would belong to the christian analog and the druid class would be present in Glantri.