Fallout 3 combat

Fallout 3 has a significantly different combat system than its predecessors, in some ways more complex because of the fully 3D environment.

Damage
The damage formula is calculated as follows:
 * $$[(Base Weapon Damage) + (Total Critical Damage)] x (Better Critical Perk) x (Sneak Modifier) x (Appendage Modifier) = (FINAL DAMAGE TO TARGET)$$

Example
The Terrible Shotgun is one of the most powerful weapons in the game. While in perfect condition, and with a Small Guns skill of 100, the weapon deals 80 damage, plus an extra 40 damage for a critical hit. However, this weapon fires 9 pellets. Because of this, when the weapon is fired outside of V.A.T.S. and scores a critical hit, the critical hit for each pellet is counted individually. This means that (if all pellets make contact), the weapon will deal 440 damage (80 base damage, plus 9 extra 40 critical damages). In Sneak Mode, this damage is doubled, increasing it to 880 points of damage. And if the player has the Better Criticals perk, the damage will increase to 1320. If the player further increases the damage via a Headshot, then that damage doubles again to 2680, enough to one-shot a Super Mutant Behemoth!

[80+(9*40)]*(1.5)*(2)*(2) = 2680 damage

VATS
The Vault-Tec Assisted Targeting System, or V.A.T.S., is a queuing system, inspired partly by the ability to shoot specific body parts in the turn-based combat system of Fallout and Fallout 2.

While using V.A.T.S., the otherwise real-time combat is paused. Various actions cost action points, and both the player and enemies can target specific body areas for attacks, inflicting specific injuries.