Normal run? All of them were easy. On legendary? All of them were easy except for Halo 2 haha. But honestly that’s what made it so fun. And then an added bonus for when I took up speed running for that campaign. Such good memories
Halo 2 is gonna take the cake on this one. Balancing issues and time to kill were absolutely bonkers. That's not even counting the Jackal snipers who could one shot kill you at any time if you didn't memorize their exact location on each map (and even that didn't always help). I always laugh when you're in the armory and the master gunnery sergeant is going over Chief's new armor and talking about how it's better in every way... and then when you play the actual game the armor is about as protective as tissue paper.
I distinctly remember trying to beat the level Gravemind on Legendary and got killed before my targeting reticle even appeared after the title sequence (haven't even tried since).. then I saw some youtuber discussing that issue and was glad to see I wasn't the only one who had that problem.