Skins
Complete the Single Player mode to unlock the Nathan Hale skin. Complete the Single Player mode with the difficulty set to "Superhuman" to unlock the MP Soldier Skin. Accumulate all skill points in a Campaign Mode game to unlock the Mechanic Skin. Complete Campaign Mode with the difficulty set to "Superhuman" to unlock the Black Ops Skin. Finish the game on "Superhuman" difficulty and achieve every skill point to unlock the Black Ops Skull skin. Unlock the Cloven Skin by registering at "myresistance.net" and entering the code provided.
Weapons
Successfully complete the game on any difficulty level to unlock some new weapons. Once unlocked, these weapons are found in various parts of the game. Find the Reaper inside a house in the level titled "Gauntlet." Grab the Backlash Grenade in from a house in the level titled "Cathedral." Locate the Arc Charger near the officer's quarters in the level titled "No Way Out." Find the L11-2 Dragon inside a tiny bunker in the level titled "Evacuation." Finally, locate the Splitter on the mall's second floor in the level titled "A Desperate Gamble."
Superhuman Difficulty
Unlock the difficulty mode of "Superhuman" by successfully completing the game once in "Hard" mode.
Other Tips
Two separate packs of Concept Art can be unlocked through gameplay. Unlock the first pack by acquiring 10 skill points and unlock the second by acquiring 20 skill points. Achieve the Ninja Medal by racking up 60 kills in melee combat. Unlock the in-game movie player simply by completing the game on any difficulty level.