It was recently announced that 343 would be bringing ODST to the Master Chief Collection. People were happy! High resolution and higher framerate ODST! And then we found out that only Campaign is planned to be ported, with no Firefight.

343, please reconsider this decision. ODST's Firefight is a unique experience in the Halo game franchise. Players were able to engage in open-ended battles in the Halo sandbox for the first time. No two runs were ever the same. Firefight's first outing required more teamwork, coordination, and endurance compared to the more arcadey matchmaking palette of Reach's Firefight, or the preset setpieces of Halo 4's Spartan Ops.

The decision is perplexing for various reasons:

Technical
ODST's Firefight is the Campaign engine. It is literally the same networking, with the same base AI. The reason your character quips as you play Firefight is because they're still running the campaign NPC dialogue engine for killing enemies. Getting Firefight to run, in development terms, is almost free once the ODST campaign engine is up and running on the Xbox One.

Fun fact: the modes are so similar that someone accidentally swapped the metadata for Rally Point's campaign and Firefight versions. The game still compiled and ran, and nobody noticed the results of this mistake until after the game came out1

MCC as an Archive
Cutting ODST's Firefight would be like cutting Halo 1's original multiplayer from the MCC. While both have a couple of warts here and there in functionality.. they're still loved by a lot of people. And it's very important to preserve the functionality of the entire game as it originally released. In ODST's original release, we had to swap discs to go from Halo 3: ODST's campaign and Firefight to Halo 3's multiplayer. Including the entire ODST featureset would finally let people enjoy the entire Halo 3 experience without disc swapping (or in this case, console swapping)

Gameplay
ODST's Firefight is a much more survival oriented mode than Reach Firefight or H4 Spartan Ops. You are weaker than the Chief. Brutes are a legitimate threat to your life. Chieftains are something to be feared. The Buggers existence are cursed every waking moment of an ODST's existence as long as they are still alive. Especially those jerk Bugger Captains with shields. You truly had to play with your back against the wall.

Completedness
While a lot of people enjoyed ODST's campaign, Firefight kept people playing after they had finished it.

To give you an idea of how important ODST's Firefight is to me, it's the reason I have my job today - I programmed Fire Team Zulu, a site built around ODST Firefight challenges. I had a ton of fun running it, and people had a lot of fun using it and exploring the limits of Firefight. Someone saw all the work I had put into that site engine and hired me to do something like it for another property. Firefight sparked a new creative path for me in my life at a time that I thought I had run out of ideas.

Halo 1 without it's multiplayer, Halo 4 without it's Spartan Ops, or Craig Ferguson without Geoff, ODST is simply an incomplete experience without Firefight. It was the first mode like it in the Halo games.

In 2009, Firefight sparked many Halo firsts and many ideas in those that developed and played it. Why not let that happen again six years in 2015? We know the music. Now it's time for a new generation to dance.