My favorite was beating the Halo 3 campaign on Legendary with my cousin and my brother. We played through every mission as normal and skipped over Cortana to move onto the last mission. After beating every other mission, we moved onto Cortana. Cortana was a beast, and it was ready to kill. It took us an hour or two to run through it. We were nearing the end, about to head for the Pelican, when my brothers headset died, shutting his Xbox off. This resulted in the game ending. We were so close. We ran through it one more time, and finished the game. While this may seem like a dim moment, the reward was even better at the end.