Call of Duty 4: Modern Warfare/Arcade Mode

Arcade mode is unlocked after completing the final mission: Game Over.

Mission Challenge
You get to select a mission and play it from start to finish with 3 lives and a limited amount of time.

Full Challenge
You play the whole game from "Crew Expendable" to "Mile High Club" with no cutscene missions and see how far you get, lives carry over between missions. You can pause the game but if you lose all your lives then you have to start over.

Score Calculation
If you lose, the final score is just your score times the difficulty (1 for recruit, 4 for veteran).
 * 5 Points are awarded for hitting an enemy without aiming
 * 10 Points are awarded for hitting with aiming
 * 50 Points are awarded for killing an enemy by shooting his legs
 * 60 Points are awarded for killing an enemy by shooting his belly or arms
 * 70 Points are awarded for killing an enemy by shooting his neck
 * 100 points are awarded for a headshot
 * 150 points awarded for destroying a tank
 * 150 points awarded for making a barrel explode
 * 1000 points awarded for shooting down a helicopter
 * 2000 points awarded for shooting Zakhaev in One Shot mission
 * 2000 points awarded for destroying a ZPU in The Bog mission
 * Multiplier awarded if you continually kill enemies (up to 8x)
 * One life awarded for completing a kill streak
 * One (or more) lives awarded if you reach a checkpoint

If you win then your final score is your score, plus the time you took in seconds times 5, plus 1000 for each life, times two if you did not die and finally times the difficulty(1 to 4).

$$Final Score = Base Score + (Time*5) + (Lives*1000) * 2 (Flawless) * Difficulty$$