Even though it's simplistic and all too often preachy, the Good/Evil binary solves a simple but fundamental problem with choice in games: letting players know they have one. It's easy to put a byline on a package about choice, but harder to define exactly what that means to the player. By framing choice in such stark terms, it lets players know what to expect. This is great for splitting narrative and gameplay, but it's far too simple to make narrative choices a meaningful or interesting part of gameplay.
via gamesetwatch.com