Compared to the earlier incarnations of the FPS like Doom, Quake and Unreal Tournament, what sorts of game-play features did Halo add or change?
They moved the gun from the front to the right side, they added the ability to jump, they added grenades, they also added online multiplayer.
How did this change the way players played it?
They used online multiplayer to get better at the game.
What sort of features were added or changed from Halo's model to make the FPS scene into what it looks like today?
Slowly adding better graphics and slowly adding better online multiplayer until halo 4.