One of biggest factors in video game immersion is the quality of the artificial intelligence of the non-player characters. In various games, the level of AI needed differs greatly, depending on genre. In shooters, you don't want enemies charging at the player, rather they should look for cover and try to outflank the protagonist. In stealth games, they should search hiding places intelligently, not randomly. In RPGs, they should use abilities best suited against your weaknesses.
However in GTA, they most just need to jump away from speeding vehicles. Or, you know, not.
These NPCs are commonly referred to as PEDs in GTA V (short for pedestrians), and have barely any role in the game more complex than running in the opposite direction of gunshots or fast moving vehicles. Of course, there are special NPCs, enemies and police forces with different behaviors, but the PEDs don't really do much more.
While not technically PEDs, the animals of GTA V have also been equipped with their own AI programming. Now, these are little more than mobile set pieces, which do their thing while in close proximity to the player. However once outside the range, they simply despawn and return into the nonexistent virtual ether whence they came.
