On every level for me, from Delta Halo onward, the Halo 2 campaign always crashes about half way through the level, usually at the same spot every time. I then have to re-start the Xbox. I don’t think this happens on a difficulty other than Legendary.
While I haven’t had the game crash on me every level, certain missions were almost guaranteed to crash like Delta Halo and Regret on legendary, especially on co-op. Others like Quarantine Zone has a de-synch bug when playing legendary co-op. I am sorry to hear that your games crashing. My advice is to run the game in the old graphics when your playing the affect campaigns or if you playing on the playlist avoid the playlist and play it on the regular campaign mode, it has helped some people in this forum in the past with this problem. Otherwise the only solution left for your problem is hoping 343 finally gets their act together and fix the campaign issues, these problems have been occurring since launch time. This option is not likely to occur anytime soon, seeing 343’s track record in their priorities in patching this game once a month.