I personally thing the only "fun" thing about halo campaigns is trying to jump up into cool sniping places, and giving everyone grav hamers and spartan lasers in multiplayer
The mission Cortana wasn't hard, just annoying and long. My favorite mission is Floodgate. I can beat it on Legendary without diein. I want to play Reach so bad!!!! I want to use the new (well old for them) sniper and the assault rifle.