As I mentioned in my Beefing Up the Fighter — Option I post on February 26th:

Many people seem to think the D&D Fighter class is too weak, especially at higher levels. While I think this is less true in TSR versions of D&D, many people disagree. I’ve come up with two simple options for beefing up the damage a Fighter does, especially at higher levels. Neither has been playtested, but both look good on paper. If you feel the fighter needs beefing up, you might want to give one of these options a try. Both options are designed with old school D&D in mind, they would probably need modification to work in 3.x and might not even make sense in 4e.

In my Beefing Up the Fighter — Option I, I gave a simple Weapon Mastery rule that raises the amount of damage a fighter does with selected weapons as he gains levels. Today I have a different way of beefing up the Fighter, special rules for critical hits. This rule assumes that you define a critical hit as rolling a natural 20 that would otherwise hit) and that a critical ht does double damage. If critical hits work differently in your campaign and you wish to use this rule, you will have to adjust to to fit your critical hit rules.

Fighter Critical Hits: While a non-Fighter character critical hits for double damage on a natural attack roll of 20 (that would otherwise hit), when a fighter scores a critical hit and its effects depend on the fighter’s level:

• At level 1-5, a fighter scores a Critical Hit on a natural roll of 19 or 20 that otherwise would hit. On a natural 19 roll critical hit, the fighter does 2x damage. On a natural 20 roll critical hit, the fighter does 2x damage and gets a second free attack against that opponent..
• At level 6-10, a fighter scores a Critical Hit on a natural roll of 18 through 20 that otherwise would hit. On a natural 18 roll critical hit, the fighter does 2x damage. On a natural 19 roll critical hit, the fighter does 3x damage. On a natural 20 roll critical hit, the fighter does 3x damage and gets a second free attack against that opponent.
• At level 11-15, a fighter scores a Critical Hit on a natural roll of 17 through 20 that otherwise would hit. On a natural 17 roll critical hit, the fighter does 2x damage. On a natural 18 roll critical hit, the fighter does 3x damage. On a natural 19 roll critical hit, the fighter does 4x damage. On a natural 20 roll critical hit, the fighter does 4x damage and gets a second free attack against that opponent.
• At level 16 or higher, a fighter scores a Critical Hit on a natural roll of 16 through 20 that otherwise would hit. On a natural 16 roll critical hit, the fighter does 2x damage. On a natural 17 roll critical hit, the fighter does 3x damage. On a natural 18 roll critical hit, the fighter does 4x damage. On a natural 19 roll critical hit, the fighter does 5x damage. On a natural 20 roll critical hit, the fighter does 5x damage and gets a second free attack against that opponent.

Note: Only the Fighter class should get Weapon Mastery. Fighter sub-classes or other fighter-like classes should not.

Like the Weapon Mastery rule, the Fighter Critical Hits rule has the effect of ramping up the damage a Fighter can do as his level increases. The Weapon Mastery rule give the fighter more predictable high damage per round when he is using a mastered weapon. The Fighter Critical Hits has a much more variable effect on the amount of damage a fighter will do with a single attack, but it applies to any weapon the fighter uses. The second option looks more complex, but I think it is more “very wordy to describe” than it is much more complex.

If I were going to use one of these rules in my campaign, I’d likely pick the Weapon Mastery rule. Every campaign is different, however, and I can thing of campaigns and player groups where the Fighter Critical Hits rule might work better. Remember, however, that I’m not convinced that the fighter in early D&D really needs to be beefed up.