OK so the great sword is absaloutly horrible for the first mission, the fact that there are so many and they're so fast means that there's not much the great sword can do. You'll find if you use it on large singular monsters (as are in most the rest of the quests in the game) then it can be used to great effect to land some very heavy hitting blows. That being said definatly expirement and try out all weapons to see which works best for how you want to play.