I’ve recently played through all the FPS Halo titles on Legendary in the order in which they were released. In Halo, Legendary was really fun, as it was a challenge, and you had to play smart and use strategy and skill to pass each level. Halo 2 was almost like this, though it was severely cheapened with the addition of Jackal Snipers, making missions require a lot more luck to pass. Also, the more aggressive Flood with energy shields put a damper on the experience.
ODST and 3 were frustrating, because a lot of times when you died, it felt as though there was nothing you could do to prevent it. Brute Shots killed so fast, and were very difficult to dodge when there were multiple enemies with them. The games had you fight up to 15 Brutes at a time, something no other Halo released to this day has done. Any section where you had to rely on a friendly AI with a vehicle (The Ark LZ fight, Coastal Highway) was an absolute nightmare, as the enemies killed you before your allies even decided to notice enemies were firing on you. It was reduced to getting lucky and hoping that your marines happened to fire at the right target, because they wouldn’t even fire if you didn’t put yourself into enemy range.
Reach had the same issue with vehicle AI, and additionally had cheap lightning fast nearly undodgeable enemy Melee attacks. If an Elite ran up to you, you better hope whatever weapon you had could kill faster than the Elite could reach you, because once it was close, there was nothing you could do. Hunters went from easy bosses in Halo CE to a good challenge in 2/3, to cheap and annoying in this game. Some of their attacks are just not dodgeable and their health was seriously increased.
Halo 4 really felt like an insult. “Challenge” was replaced by enemies having extremely high amounts of health and also undodgeable attack patterns. When a Knight started it’s tele-charge at you, there was so little you could do to save yourself. The enemies with the one-shot-kill snipers were now Knights, rather than Jackals. You could no longer just spot the enemy and quickly dispatch it before it killed you. Hunters again were buffed.
Halo 5 at least fixed bullet-sponge knights and replaced most of them with less Bullet-Spongy soldiers, and this was good, but in order to balance the game around your squad, your shields were considerably weakened, giving you even less resistance against fast-killing, highly-armored enemies in the game. Finally, Hunters are no longer feasible to kill solo. Barring extreme luck and the fastest-most-perfect-lightning-reflexes known to man, you cannot dodge Hunter melee attacks anymore, and even their Fuel Rod is much tougher to dodge. You cannot get behind them, and unless they happen to target your allies instead of you, you’re screwed. Your deaths don’t feel like your fault anymore. They feel cheap, and there’s a difference between challenge and cheapness.
Please, for Halo 6, try and make your campaign feel less cheap.