Halo 4's Spartan Ops mode began life as a "Firefight-type mode" in which players completed randomised missions on a single map, according to lead designer Chris Haluke and senior designer Greg Murphy. Eventually, however, 343 decided that fixing mission content in line with the over-arching multiplayer narrative would make for a better experience.
"It originally was a Firefight-type mode, where it wasn't always about killing all the enemies," Murphy explained in a Halo Waypoint interview. "Some missions would be get an item (like a bomb) to the bomb spot, kill the leader, capture the item, etc. But it was more arcadey and meant to be replayable.
"Each map would have the same four or five types of missions. When you played them, it would randomly pick four missions on four different maps, and your party would play through them. We got back to this concept, then onto just concentrating on the five missions a week, then making the missions story driven."
"One of the main changes or evolutions with Spartan Ops was the importance of narrative and tying all of Halo's multiplayer together with a story that matters," added Haluke. "Narrative is an integral part of Spartan Ops, and this truly began to come together at a critical point in production when all the pieces began to fall into place. Working so closely with our narrative team has been an incredible experience, as we all get to feed into the ideas and storylines that ultimately shape Spartan Ops.
"The best way that it changed was going from more arcade-like "random" missions where you would accomplish the same goals, just on different maps in a very generic way, to something story-based, with each mission featuring a unique story, VO, goals, etc," Murphy concluded.
I'm beginning to warm to Spartan Ops after a shaky first impression, but I have bones to pick with all this. Numero uno - sorry, 343, but your original concept sounds like it would have soaked up a hell of a lot more of my time than the final article. Numero duo - the narrative holding Spartan Ops together is pretty sketchy, by my lights. Mission narratives have too little to do, right now, with the overarching CGI narrative, and mostly take the form of radio chatter, which mostly takes the form of advance notice of enemy movements and yelling about Ordnance Drops.
I seriously doubt most players would miss that on-going plot if it meant more in the way of replay-friendly missions. Besides, the two things aren't mutually exclusive. Look at Mass Effect 3's Galaxy at War Mode. There's a storyline there, but it doesn't stop the individual battles being fun.