These 2 things are what kept me playing Halo 3s campaign even after initially completing it a few times. Searching and hunting for these may have taken a lot of time but was hella fun to do especially with mates. I don’t know why they were removed (skulls specifically - they still had eastereggs - but bare boned and lack lustered in comparison to H3s ones) because they gave a reason to go back on the campaign! (after beating it multiple times)
Hope 343 add more wacky and innovative easter eggs in the campaign (could also do for MP too) and hopefully they put skulls back in to make the campaign more challenging! (eg… the iron skull would restart a checkpoint if even a team-mate died - risk but reward!) Plus perhaps do another armor unlock for capturing all skulls - like H3 had - get all 13 and unlock the Hayabusa armor. This motivated me to find the skulls back then - and surely will motivate people now as-long as the armor looks good!