The biggest addition is likely the huge new content portion of the game. In a meeting yesterday, Molyneux reported that the game will be a third bigger than the Xbox version of the game. While he doesn't want to give away details on the extra parts of the gameplay just yet, he did mention that players who noticed the door right outside the Heroes Guild in the Xbox game will have also noticed it was closed and locked. The PC version will open that door up along with everything behind it. Apparently that includes a dragon and a completely new land for players to explore.