I beat this on legendary as a kid before you were born. It’s difficult but rewarding. It has difficult sections, but you develop a flow and strategy after you pour hours into it, and that’s when the game truly transcends itself. Legendary forces you to master the game’s mechanics and be tactical with your weapon pick ups. It forces you to be savvy with your nades and git gud with “bad” weapons. It forces you to keep a fast pace and commit to your movements, because unlike other FPS, your steady, slower pace in Halo means you aren’t turning on a dime. Most difficult section is probably the library, which can indeed be maddening.
Halo 2 is harder imo, fucking jackal snipers.
Halo 3 is probably the easiest but that also has it’s moments.
Halo trilogy, especially the first one, is probably the game I’ve beaten the most times on the hardest difficulty. What a game.