As much as I liked Firefight, I have to give my side to Spartan ops... If it receives some improvement. Firefight I liked because you got to hold down against continuous waves of ever stronger and more powerful enemies that are aided by the skull system to absolutely wreck you if you're not up to the challenge, the fabulous editing in Reach was good too. But Spartan Ops, I love it as it is a continuation of the story, that there is a reason that you are holding down against the opponents, not "if it bleeds, shoot it."
If they increase the SO 's storylines more, along with cutscenes that involve you and a better look at the situation itself, it will be absolutely perfect. 10 second clips of a pelican landing is not a story, sorry. With a little tinkering, it could be a very popular mode, perhaps more than firefight... But I'd like to talk skulls, as well.