Mook: How much of an impact will players be able to make in the war of evil vs. good. I.e. will players be able to help NPC turn the tide of the war, resulting in a change that impacts all players here on forth and/or the face of Norrath?

Good and evil will always be in a constant struggle for control over the people of Norrath. There will be certain actions that players can take to sway the pendulum one way or the other, but not in a way that removes the accessibility of content. Player actions will open new possibilities, not close them off.