I don't think the Halo 4 campaign is hard at all, it's just not fun.
Exactly. I can't name many places in the Campaign where I had cleared the area and felt accomplished. It's funny because many of the Knight setups on the final level are somewhat similar to the Brute battle in the barracks in Halo 3. But just look at how much better the Brute fight is from the start.
- clear distribution and distinction of different Brute classes
- while not a wide open space, the weaponry and equipment allow for interesting approaches to the fight
- you can clearly see your goal, with a big fat Brute Chieften awaiting you
- you can obscure sight lines, and power weapons placed in certain positions allow for (if you choose to use it) a battle plan to attain it
Everything about that battle is awesome. In Halo 4, a similar battle quickly turns into a cluster f because you have all these Knights who look so damn similar, possess different weaponry and abilities, and yet they all just blend together. You can't really keep tabs on them all that well. And for all you know, that Knight you think is only holding a Light Rifle behind the pillar actually pops out with his incineration cannon and blows you to bits. Or you rush with a scattershot and suddenly a Knight does a force push (I had never seen this until the last level) and forces you off the ledge. The encounters just don't allow flexibility or unique opportunities to arrise in combat.