I've heard that in the first patch released for this game (way back in the beginning of 2010), two-handed weapons were made much better than they are in the unpatched game. What exactly was changed about them to make them more viable?
In one of the updates it was changed so that opponents in the path of your swing would take damage as well as the target. This helped with all melee weapons; two handed swords just got more out of it due to their longer reach.