The announcement trailer was absolutely incredible. When the chanting chorus was playing (with female vocales) in the end, I lost my shit. Unbeliveable cinematic and larger-than-life.
They totally created this sense of the world is ending and its all over and its just a desperate and hopeless attempt to go down in flames as Chief just plummets from space like an emotionless cyborg enhanced super soldier.
Which spoke to what I was missing about the games earth scenes when it came out. The earth levels had no civilians running away, no mountains of corpses. It was a totally abandoned (but well designed) series of levels.
When I saw that announcement trailer I thought it would be like billions of people would have died. That's how you'd imagine an invasion of earth would have looked like.
HL2 that came out in the same year, was a game where I was not invested emotionally in the grandness of the story or the characters, but undeniable the immersion factor from how the fascist takeover of the world was so much more unsettling as you saw many npcs and non-soldiers get killed, suffer, be tortured or controlled.
The Halo 2 announcement trailer was absolutely incredible. Saw it countless times. had the trailer music (ripped audio) on my Ipod from Limewire. That was life back in the end of 2003.