Once again players assume the role of Gordon Freeman, a scientist destined to save the Earth from hordes of gruesome alien attackers. Half-Life 2 takes computer games to a new level of realism with incredible in-game graphics that recreate familiar-looking city streets, and blend them with strange and grotesque monsters, resulting in a believable and at times unsettling environment. Objects and characters feature accurate physics properties, behaving with the appropriate mass, density, and physical properties of their real-life counterparts. Extremely intelligent computer AI result in enemies that plan, adapt, and respond to the player's actions.