Piratecat said:
I also tend to think that it's more frustrating to negate a really effective hit by the PCs against the bad guy.
I would agree - but it's important to understand the context of the mechanics.
In the James Bond 007 RPG, you used a % system for determining strikes. (It was a really good system, too).
Say you had a 50% chance of success:
01-05: Quality 1 Success
06-10: Quality 2 Success
11-25: Quality 3 Success
26-50: Quality 4 Success
51-00: Failure.
(That's from memory - I'd have to double check, but it was something like that). Quality 1 Successes were basically criticals.
A Hero Point used by the PC could increase the success by one rank. (From Fail to Q4, from Q4 to Q3, etc.) They could spend multiple points.
A Survival Point used by the NPC could decrease the success by one rank. (From Q1 to Q2, etc.) Again, multiple points could be spent.
Thus, on a Q1 success, the NPC would have to spend
four Survival points to negate it utterly. Within the context of the game, it worked brilliantly. Most NPCs had no Survival points - only the main henchman and villain, and even then they didn't have that many. (Jaws has 10, and he was the best. Think about the ridiculous escapes he had...)
In Spycraft/Stargate, an Action Point used by the villain cannot tone down a critical hit, but it can cause an attack to miss altogether (by the modification of the Defense score).
However, the same applies to PCs: a critical hit in Stargate cannot be avoided, and if the GM chooses, the PC is toast.
In D&D, if you permit an Action Point to boost the AC, you can reduce the effectiveness of a Critical Hit, by making it less likely to occur.
Cheers!