You can see examples of my house rules for d20
Modern here and for
Flashing Blades here.
If you look at each, what you'll find is that my house rules fall roughly into the following categories:
- rules for actions not specifically covered in the original game (frex, parachuting for d20 Modern, venality in Flashing Blades)
- expanding on existing rules (frex, skill synergies for d20 Modern, background details for Flashing Blades)
- rules which offer new or revised options for charcters (frex, new and revised skills for both games)
- rules for items or equipment not available in the original rules of the game (frex, mapmaking software for d20 Modern, blunderbusses and galleys for Flashing Blades)
- rules which add color to a specific setting (frex, the Feral starting occupation for a d20 Modern 'Darkest Africa' game I contemplated running, the more historically accurate lists of Royal Army regiments and knightly orders for Flashing Blades)
My personal philosophy of house rules is to stay as close to the original intent and implementation of the published rules as I can: for example, instead of adding a 'Parachuting' skill to d20
Modern, I made it a function of existing skills applied to the activity, much the way Balance is used in that game to handle riding a bicycle. I think of it as working with the grain of the game, making house rules that are easy for the players to grasp because they tweak the way existing systems work, rather than replacing them with new systems altogether for the most part.
I admit I'm a bit puzzled that some gamers take issue with house rules. Much of what you see in my own house rules are adding features which don't exist in the original rules; are gamers supposed to just ignore aspects of the game world that the designer didn't cover? Should I ignore Barbary corsairs and crusader knights because there are no rules for galleys in
High Seas? Can no one jump out of plane in d20
Modern because skydiving isn't in the core book?
I'm a firm believer in rulings before rules, but in some cases codifying a ruling as a house rule makes it possible for a player to better understand how the game-world works in a way that her character would, and allow the player to make an informed decision thereby, such as taking ranks in Jump for a character who enjoys skydiving.
I also believe house rules help to bring the game-world to life. Once upon a time, long, long ago, 3.0
D&D prestige classes were intended to be used for this very purpose. For my
Flashing Blades campaign, I re-vamped the composition of the Royal Army regiments and the knightly orders expressly for this purpose; the core rules present generic soldiers and knights that are intended to cover the whole of 17th century France, and instead I chose to drill down a bit and make them (1) better conform to their historical peers in the specific period of the campaign and (2) increase the options available to the players and their characters while (3) still keeping close to the way the rules are presented in the core rulebook.
So no, I have no problem with house rules. I use them, and I expect the referees of the games in which I play to use them.