In The Witcher, Geralt should use the Strong style of fighting against these opponents. If you find yourself swinging way too many times to kill an opponent, it is probably because they require a tougher approach. How can that be you ask? No one is tougher than a witcher... It is because you are probably using the Fast style of fighting which just chips away at hit points and your opponent has a lot of them. Switch to Strong style (by using the Z-key or clicking on the Strong style icon) and things will proceed much more quickly. Spoiler warning: Significant plot details follow.