I play on Legendary, usually with just one other person since we're on the same connection. We are both quite competent at Halo. Keep that in mind. Here are a few things I think this episode in particular totally fucked up. Fuel Rod Guns on every fourth enemy, usually on Elite Generals. Every Covenant mission having multiple instances of "well fuck, the drop pod is right on top of us, too bad there was no indication of that! *respawn*" Chapter 3 dropping players right at the start into a mass of high-level enemies, including an FRG General and four (!!!!) Jackal snipers, which means you're basically boned the instant you land. Binary Rifles coming somewhere out of a mass of Crawlers without any warning other than the tiny red circle in a group of indistinct silver shapes and tiny orange lights (why don't they have the laser sight from MP?) Chapter 4's Knight spawning trigger volume being two feet in front of where they spawn. And the Knights spawning in are all Battlewagons so the player that triggered them has to make a mad scramble backwards, if he can survive their often-instakill first shot. That chapter pulls that same bullshit twice in a row. Chapter 5 allowing a single Knight to spawn 8+ Watchers if you don't hit him immediately as he spawns (This is being literal. I counted.) Chapter 5's "go hit this button in this room" objective where a dozen Crawlers and a Knight spawn all around you the second you hit the middle of the room. It was shitty in Doom 3, it's shitty here. I'm actually glad there aren't finite lives in that, because the game screws the player over so many times per chapter that I don't know that I'd want to ever finish a single episode.
And frankly, the encounter design, often because of some of those elements I listed, is kind of bad. Instant-kill weapons should be a rarity. They are not fun to fight against. Look back to Halo CE. Every Elite in that game carries a Plasma Rifle for a very long time, and then you find that every once in a while, there's one with a sword. It's tense, it's fun, it's special. In Halo 3, Hammer Chieftains were rare and special, and ended up being some of the most fun in that game. When you dole out things that change up the combat flow so dramatically in every single fight, often multiple times per fight, they lose their sheen and it gets boring and frustrating.
Episode 3 was fairly strong in comparison, but there needs to be a fundamental change in how they're designing those fights to keep me interested.