Bungie's composer has said the studio's renouncement of Master Chief and Halo has been liberating - and a little frightening.
"The hard part I think was we almost peaked too soon," Marty O'Donnell told Industry Gamers.
"For me, musically, I had this great theme. The monks were the iconic thing and there was a point where I thought, 'Should I come up with a new iconic theme for each one of the games or should I just try to build on that?'
"That was probably the most difficult thing... it still needed to sound like Halo for each one of the Halo titles."
Balancing originality with the series' familiar musical score was a challenge, which made those titles without its iconic hero something of a holiday for the composer.
"Go forward about 7 years and we started working on ODST. What was nice about that was it wasn't the Master Chief story and it wasn't taking place on a Halo," O'Donnell said.
"... And then Reach is another one where I could drift away from the classic Halo themes and just make something that was unique to the Planet Reach and to the soldiers that were on Reach that sacrificed their lives and come up with a bunch of new music for that."
Now, of course, Bungie has ended its deal with Microsoft, left the Halo IP in 343 Industries' hands, and begun work on the first title of a ten year agreement with Activision Blizzard, which is a little scary.
"I think the other thing I would say is bittersweet... walking away from the Halo universe... I had so much music that I'd created over the last decade and walking away, I go, 'Well, all right. That's the end of that. We can't even pull from that music any more for anything in the future at all. It's all for Halo.'
"So essentially I'm just taking all those CDs and - I don't know what there is, maybe 40 or 50 hours of music - and just putting it on the shelf and moving forward on to something brand new.
"It's kind of a relief because from a creative standpoint it's great to just have an absolutely blank sheet of paper, but then on the other hand blank sheets of paper are scary to creative people. I'm not saying I have writer's block, but we'll see..."