So according to fluff and all that, Force Weapons can be made into a bunch of different types whereas swords and staffs are the most common and easiest to get hold of, and Nemesis weapons being used by the grey knights (probably not too easy to get a hold of, if they're the only ones allowed to have them?).
Then, how would you stat up for example a force halberd or something similar "cool" and not-so-boring force weapon?
You think a grey knight as able to parry with their halberds? Because parry would be nice to be able to do still, without forced to use Iron Arm.
). If a Great Weapon is going to not be unwieldy, I'd rather there be a serious price to pay for it - In this case, I again mention the Relic Blade as a good starting point (Lots of Renown and Requisition required, and for that price, a weapon that hits like a bag o' bricks).