Rockstar's attention to detail in the GTA games has always been a major point of praise. The new-gen version of GTA 5 elevates that even further with its upgraded graphics and increased NPC count.
The short below by The XXI captures the life in GTA by night. All those NPCs going about their lives, all of which you've probably missed in your pursuit of a new gun or a fast car.
The city looks best at night, but what adds even more weight to all the scenery is how NPCs act like how you'd expect regular pedestrians to act.