Okay, so when I got back into RPGs in the early 2000s I bought D&D 3rd Edition because it was the "current" version and because the details in the reviews I read all sounded pretty good. After I bought it and gave it a proper read I was not at all happy with the way critical hits were handled. Granted, they were at least putting some thought into it instead of just making it double damage on a natural 20. But all they really did is make it a lot more fiddly and complicated, which is not what you want with combat mechanics (because combat should be fast) and played into the hands of min-maxer types.
The problem with the original idea of double damage on a critical hit is that if the damage roll is low the "critical" hit could do less damage than a normal hit. For instance if your regular damage is 1d8+1, then if you roll a 1 for damage your big, scary critical is just 3 points. So I decided that critical damage should be seriously dangerous, but that the procedure should be simple.
After some research and experimentation I decided that I would scrap the 3E/Pathfinder approach and run it like this:
- critical hits only occur on a straight natural 20 on the d20
- damage is full damage plus a regular damage roll. Example: if regular damage would be 1d8+1, then a critical hit would do 9 + (1d8+1) points of damage.
That's simple and effective.
I also allow players the option of rolling a hit location die (the kind with the hit location actually on the die--no charts needed). Then I add some extra effect based on the location. A head crit can result in stunning, being knocked unconscious, or possibly instant death. A leg hit might knock the victim down or make that leg useless until healed. I prefer to improvise these extra effects based on the situation and on "what would be cool" rather than use charts or cards. It seems to me that charts and cards often give results inappropriate to the situation and then we have to fudge things to make the crit result fit.