Part of the satisfying nature of it is exactly in how rarely it gets invoked, like, two or three times per gaming session at most. It definitely throws in just the right amount of unexpected "spice" detail that makes combat exciting, unpredictable, and truly dangerous (without generally encumbering the process or the pacing). It throws a very nice curve ball into the standard d20-and-damage combat sequence, yet it's still an objective mechanic (not just DM fiat). And we have yet to see the exact same "special" result twice in the time that I've been using these tables. One of the things I do is, even after a 1 or 20 are indicated, grant the victim a saving throw to avoid going to the tables -- this nicely avoids oddities like high-level fighters constantly fumbling their sword, makes powerful monsters or established PCs difficult to take down by this technique, etc.
I haven't presented the tables here in the past because they're simply straight out of an old Dragon Magazine article -- a submission by the otherwise unfamiliar name of Carl Parlagreco, "Good Hits & Bad Misses", in Dragon #39 (July, 1980). To my knowledge, this is the only classic Dragon article dealing with the issue of critical hits; I think it was a short time after this was published that Gygax wrote one of his screeds, especially pointing out critical hits as a corruption of core D&D play. But I've found them to be extremely satisfying in my OD&D games. (Note that I almost totally ignore the text rules, but use the tables as written.)
Note how nicely this is laid out, from the era when meaty Dragon articles might only take up 2 pages as shown here (I print this out on one sheet of paper for my DM screen). It even has a thoughtful space left for "Notes" for your own refinements to the system. Here's what I have written in mine:
- On natural "1" or "20", target saves vs. paralysis (level+3) or consult appropriate table.
- Fumbles: ignore indicated Dex checks.
- Liberal interpretations necessary: negate/change unreasonable results.
- Delayed death results negated by magical healing.
- Undead immune to effects except head crushing/decapitation.
Edit 1: Also, consider making the victim roll the d% dice to determine the final critical-hit effect. Holy god, the look of horror on the player's face when they have to do that is unparalleled.
Edit 2: Get a PDF copy extract of these tables here.