The
Halo: Reach survival mode, Firefight, pits the player against relatively dull bullet sponges. To compensate, matchmaking relies on ridiculous loadouts, damage modifiers, and a large, if not infinite, pool of lives. The only plausible explanation I can think of for playing Firefight in its current form is that is offers a sizeable pay out of credits. Campaign lacks even a plausible explanation.
However, like many aspects of
Halo: Reach, both Campaign and Firefight are frustratingly close to providing a great gameplay experience. The levels, with regards to movement and cover, are well designed (unlike
Halo 4), and the AI can flank, rush, and fall back, when necessary. The problem is that the current set-up does not lend well to any of these AI behaviours. You can choose to face dim witted and weak opponents, or more coordinated foes with near impregnable shielding; neither option is particularly enjoyable and both restrict variety.