1) The arm swing angle looks off. It doesn't look like a swing, it looks more like a blocking action. And at that angle, seems like it wouldn't generate that kind of force- with what looks like a big heavy weapon.
2) The "WHAMP" edit makes the sword look like it's made of mud.
3) I suggest either accent the swing with motion blur or increase the effect of the hit on the monster and not the swing on the blade.
4) If it's not the climactic killer blow, this is a minor issue, overall.