I was thinking about ways to make larger weapons, greatswords in particular, different and worthwhile without giving them a bigger damage die. As I did this bit by Giacomo di Grassi popped into my head
Which made me think somewhat of the way shotguns are portrayed as 'Street Sweepers' and the like, and how suppressive fire works. Simply put, a person with a large sword can stand against many lesser weapons. A large space can be covered with one if one were inclined to made broad sweeping blows.The two hand Sword, as it is used now a days being four handfuls in the handle, or more, having also the great cross, was found out, to the end it should be handled one to one at an equal match, as other weapons, of which I have entreated. But because one may with it (as a galleon among many galleys) resist many Swords, or other weapons: Therefore in the wars, it is used to be place near unto the Ensign or Ancient, for the defense thereof, because, being of itself able to contend with many, it may the better safeguard the same. And it is accustomed to be carried in the City, as well by night as by day, when it so chances that a few are constrained to withstand a great many.
Aside from doing something boring like a bonus to fighting defensively, which could be done I guess, I thought about the reason why it can withstand against many. It threatens to delimb anybody in reach, ignoring attacks of opportunity style rules (which if you aren't using might be cool to allow with greatswords and similar weapons when used defensively), I've considered treating them similar to a shotgun or automatic fire, attacks against everyone in reach at a penalty (-2 sounds about right).
Large swords cover a large amount of space and were used to defend areas because of that.
Possible extra bonus when used defensively.
Possible free attacks when entering and leaving the zone of death.
Recommend "shotgun" style attack all in front at a penalty (-2) for reduced damage.
Addendum: Matt Easton did a video on the zweihander 4 days after I wrote this.