I'm not sure why the 'completely' is in there, but the 'new game' means it is being released separately. As Windemere said, there were many changes to quests, skills, abilities, etc, that it would be impossible to maintain save compatibility, in addition to the updates to the game engine (switching to DX 11 on Windows rather than 9c, etc).

The Enhanced Edition is free if you own D:OS; Swen wasn't trying to 'sell this enhancement stuff'.