When we started out campaign we neither expected to be recording actual play episodes, nor did I know True20 very well. This led us to adopt some house rules. I have adopted house rules with every system I've ever ran, and of those I suggested, a couple were adopted. A third was adopted after our first session.
I've compiled the house rules below and the reasons I adopted them.
1. 2d10 replace 1d20
Mechanic: Whenever a d20 is required for task resolution, 2d10 are used instead. A natural 2 (both dice present a 1 as their result) replaces a natural 1. Natural 20s (both dice present 10 as their result) for an attack roll is an automatic critical, and does not need to be confirmed. In all other ways, natural 2s act as natural 1s and natural 20s act as natural 20s.
Reasoning: If I understand the math correctly, a single die provides a total variation of results, in that one number is just as likely to appear as any other number. Given this, until one has bonuses upwards of +10, it is just as likely to fail horribly as succeed, even at a task with which your character is proficient. 2d10 creates a greater likelihood of medium results (8-12) with less and less chance of extremes (natural 2s and natural 20s are extremely rare, hence the lack of critical attack confirmation). This also means that bonuses have a greater impact on outcome.
2. -1 penalty per Wounded condition
Mechanic: For each Wounded condition a character receives, the character has a penalty of -1 on all checks, including attack rolls and Fortitude, Reflex, and Will saving throws, but not Toughness saves or Constitution checks. The penalty is cumulative, so if a character has 3 Wounded conditions, the character has a -3 penalty.
Reasoning: I prefer a system that models deteriorating physical capabilities due to physical damage. In the d20 system, physical damage has no impact on a character until that character is disabled. Basically, the character goes from 100% to 0% in an instant. True20 is better, as a character with a Wounded condition has a -2 penalty on checks. I wanted something to show the continued punishment a character might be taking is continuing to impact on that characters performance. As a character can have multiple Wounded conditions, and those are easy to keep track of on the character sheet itself, it seemed an easy way to model deteriorating capabilities.
3. Iconic Weapons
Mechanic: Each character chooses one type of weapon (sword, axe, bow, etc). With that weapon, the character gains a +4 to attack or defence (decided at the beginning of each combat round). Further, an iconic weapon always has +4 damage.
Iconic weapons inflict no penalty when used for ranged or melee combat, so a sword can be thrown without penalty and a bow can be used in melee without penalty.
The combat bonus and iconic damage can only be used by one weapon per round, so if a character is fighting with two weapons, only one of the weapons gains the +4 combat bonus and damage rating of +4. The second weapon would not gain the +4 combat bonus and would use the normal damage rating for its weapon type.
Reasoning: In movies and books, heroes often use specific weapons for stylistic reasons. By setting the damage rating at +4, it allows for a player to choose a weapon based on character concept or style and not be penalized. All weapons end up the same, to the weapon choice becomes a stylistic one.
Many heroes are also known for their skill with a particular weapon. While the weapon skill could be modelled through the use of feats, I wanted to provide the characters with a level of cinematic skill without forcing a payment in feats. Further, fiction often portrays characters using weapons in a fashion for which they were not designed, such as throwing a sword or clubbing an opponent with a bow. To model this, I removed penalties for such uses.