The game on legendary to me is underwhelming. Therefore, no replay value on co-op and let alone with all skulls on.
What bothers me the most is the AI of enemies and friendly Marines and the spawning and despawning of enemy manned ground and especially air vehicles.
There is some really lazy work around FOBs. What is this crap with Marines standing under the Pelican as it drops vehicles. They just wait to be squashed or to get catapulted out of the map. In Halo 1-3 Marine units were inferior to Elites and Brutes, and where in Halo 4 Marines were useless at best, here they are super soldiers. A Marine solos 2-3 Brutes, and Elites. Insane.
Enemy AI on legendary is weak, predictable, slow, a joke really. In Halo 1-3 you had to be on your guard and plan ahead, here you can just grapple hook into the fray and kill a full squad of jackals/brutes/grunts/elite mix.
Sometimes I fly this weird wasp thing. So much into the future and we fly a snail that is supposedly very maneuverable, but it really isn’t. And suddenly Banshees spawn left and right out of thin air, and many times as I keep “dog fighting” (if you can call it that), half the times enemy disappear also into thin air.
The whole campaign feels rushed. This open world approach needed way more work. Having a hard tine figuring out which is worse, this or Halo 5 campaign.