William Shatner's TekWar is a 1995 first-person shooter video game derived from the TekWar series of novels written by William Shatner. It was designed using the Build engine.
The premise details an ex-cop who is hired to be a hitman whose mission is to exterminate drug dealers who peddle "tek". The two most distinguishable features are the hub-based level system (all the levels are interconnected by a subway station), and the fact that all of the non-player characters (NPCs) in the game (enemies, policemen, civilians) are shootable. When the player draws his gun, policemen shout: "Freeze! Drop your gun!" before they start shooting at the player. When a policeman or enemy is killed, their ammo can be picked up. When the player aims at a civilian, he/she ducks and screams: "Please, don't shoot!" When any NPC is shot, a blood spot appears on the wall behind it. If an NPC is shot with one of the stronger weapons in the game, they will explode into gory bits.
The games narrative took place using cutscenes at the beginning and end of each level, featuring Shatner himself (in character as Walter Bascom) as the narrator. Cutscenes varied depending on the player's performance during missions: if the player didn't shoot any innocent NPCs, managed to take out the TekLord in the mission, and didn't raise any tension (i.e. walking with his gun drawn), Shatner would deliver praise. On the other hand, shooting NPCs or aborting the mission caused him to threaten to have you put back into cryo-storage.
Source: Wikipedia, "Tekwar (game)", available under the CC-BY-SA License.