In the original stories, John was a flat character to emphasize by contrast Sherlock's extraordinary qualities. In this BBC incarnation, John is just a constantly confused but compassionate person, to emphasize by contrast that Sherlock is crazy
The best thing about this is that John is completely comfortable with Sherlock holding a gun to his head. John, the ex-soldier who has already been shot once, is completely comfortable with this situation. Who didn't teach Sherlock gun safety?
Hudson by throwing a man out the window. Lestrade: "And exactly how many times did he fall out the window?" Sherlock: "It's all a bit of a blur, detective inspector. I lost count." Also that Lestrade is the least irritating officer lol