Halo 2 anniversary added some really cool Co-op skulls in Bonded Pair and Masterblaster. They added a neat new way to play through the campaign a second time with a friend and just helps keep things fresh.
I’d really like to see this concept expanded in the next game.
Just more skulls in general would be a great thing to help spruce up the game and add that extra bit of replayability, but those co-op skulls that make each player have a certain role to fill would be really cool.
Who’s with me? Who wants more skulls?? Heck, even skulls in custom multiplayer would be cool!