While the World of Darkness mechanics are very solid "right out of the box", it's simple and flexible enough to accommodate numerous modifications. Following are several house rules which can be patched into your WoD. These rules are modular, and not dependent on each other; you can choose to use my rules for firearms and Defense, but not the wound penalty or dramatic failure stuff. Use what you like, and discard the rest. And feedback on this at Facebook or MySpace would be appreciated -- if my rules either improved or broke your game, I'd like to know.

Dramatic Failures
"Botching": If half or more of the dice show results of 1 on any roll that results in a failure, the character suffers a dramatic failure -- just as if she rolled a 1 on a chance roll. Rationale: By being limited to a result of 1 on chance rolls, dramatic failures are too predictable and uncommon.
Chance Roll Overflow: Die pool penalties that would reduce a character's die pool to below zero dice "overflows" into an increased chance of dramatic failure on the chance roll. A penalty that reduces her to exactly zero dice uses the "official" rules for dramatic failures: she suffers a dramatic failure on a roll of 1 on the chance die. If she would have had -1 dice in her pool, however, then a result of 1 or 2 on the chance die results in a dramatic failure, while a -2 dice die pool indicates a dramatic failure on a roll of 1-3; as the die pool decreases further, the chance of dramatic failure scales accordingly. If by any chance a character (God forbid) is penalized -9 dice or more, a roll of 10 is treated as a simple failure, not a success.

Defense
Defense Rating: Defense is the average of Wits and Dexterity, fractions rounded down. Rationale: Really fast reflexes or superb reaction time can mitigate the lack of the other.
Defense vs. Firearms: Half Defense (rounded down) is applied against Firearms attacks, save for those made at point blank range (to which full Defense applies). Rationale: While I'm not big on the idea of some everyman ducking and weaving through bullets ala Neo from The Matrix (though some high-end supernatural powers might allow this), it's common sense that dodging around or moving at all makes you harder target to hit. The rules as written don't account for that: by the rules, a running person is as easy to hit as a stump. Characters shouldn't get their full Defense vs. ballistics, however, which is why Defense is halved.

Damage
Realistic Wound Penalties: Wound penalties begin sooner, with a -5 penalty in the last Health box and counting down from there in one-die increments (instead of -3). If a character has five or fewer Health, then penalties are downgraded so that the first Health box recieves no penalty, the second one -1, the third -2, and so on. Rationale: Between pain and tissue damage, even a grazing wound should impair a little. Exception: Because of their dead flesh and lack of vital organs, vampires receive a -3 penalty in the last Health box (i.e., the canon default is used for them).
Expanded Wound Penalties: Wound penalties are applied to Initiative, Defense and Speed, just as they are to rolls. Rationale: It's rather hard to respond quickly, move out of the way of an attack or run quickly if you're chopped to ribbons, wouldn't you think?

Compounding Penalties Taken separately, Realistic Wound Penalties and Expanded Wound penalities won't pose a big problem for players; taken together, though, they can be prohibitively harsh. Unless Storytellers plan on running very gritty games, it's probably a good idea to go with one or the other house rule, and not both.

Impairment: For grittier combat, some Storytellers may want to simulate the possibility of maiming, crippling and scarring. This sort of thing can and does happen in the real world, and would in the World of Darkness as well (where the sort of violence that leads to such is even more prevalent). While making the setting more brutal, it also adds potential drama to WoD stories; the very possibility (however remote) of people being left messed up for life -- with broken bones, damaged equilibrium, brain swelling, ruined looks and the like -- makes fights seem more real and the consequences more dire. Some sort of mechanics should be in place to reflect this, even if the Storyteller elects not to use them. This sort of thing may not be appropriate for all games, so use at your own risk.
A check using [remaining Health] +1 die is made for characters that have half or more of their Health boxes filled with lethal or aggravated damage; this can be made during the fight as the damage is dealt, or after, as appropriate. Those that suffer Incapacitation from lethal damage roll only one die (a chance roll). Willpower may not be spent on this roll. Success indicates the character suffers no impairment from his injury, and heals normally. A failure indicates an Attribute dot is lost or an appropriate Flaw is gained, chosen randomly or by the Storyteller; this lost dot or Flaw "heals" with the associated damage. A dramatic failure is treated as a failure, but the stat loss or Flaw is permanent; however, the character may heal the Health box damage associated with that injury as per the normal healing rules.
The more severe the injury, the greater the chance of debilitation, and the roll needn't be made by those that avoided excessive amounts of lethal damage. In addition, the impairment should reflect the nature of the injury: someone beaten to a pulp with a claw hammer might suffer a loss of equilibrium (lost Dexterity), brain damage (lost Metal Attributes), or Social roll penalties (his face is a scarred mess).

Armor
Each three full dots of Strength reduces Defense penalties from armor by 1. Rationale: Stronger characters can move around more easily while encumbered, and aren't as weighed down as much as someone of lesser strength.