Deadguy said:
a sudden death against which there's no defence can really spoil things. And I have a hard time denying smart, well-equipped NPCs the use of an item that is, as you say, an extremely good tool against powerful foes (the PCs).
I agree with both of you. Vorpality. Cool and deadly. In the upcoming Doorway Games release, entitled, "The Executioner's Blade," (due out soon for release in PDF, via RPGnow) we deal with that issue in the following manner:
Versus monsters of any size without melee weaponry, or large creatures and above, the successful vorpal attack slices the head right off. For creatures of such size the length of the sword would never be able to sever it, there is a sudden burst of energy which extends the blade's cutting edge to needed length (just like magical armor resizes).
For creatures which engage in humanoid-like combat, using melee weapons, or the equiv, such as monk attacks and defenses, the vorpal blade must have two successful attacks in a row to result in a successful vorpal attack. Prior to this, the DM is encouraged to either instruct the players that the blade appears very sharp, or else have them roll spot checks under less than well lit, or chaotic conditions.
This adds drama and adds purpose to the DMs placement of NPCs with Vorpal blades. The NPC engaging the party with a threateningly sharp blade is more likely tp be protecting something, or blocking progress towards a goal, which adds a sense of dilemma and causes the players to engage with care - adding texture to the ensuing fight. Hit once, they may want to back away lest the next blow nail them. Add multiple attacks in a round to this and the Vorpal blade can still be a very mean attack!