Spoilers!!!
I like Locke, and think it’s fine to have him playable in the campaign. But there were too few missions that involved Master Chief. I even bought the Halo 5 Master Chief controller in anticipation of playing the Chief in the campaign, but I was disappointed of what little he was playable in the game.
Other than that the campaign maps were setup really well. I only play on solo, but overall the fireteams’ ai was pretty good. I think they mostly need to be improved during boss fights. I may have been doing it wrong, but I did finally beat it solo legendary. It’s just during the boss fights I had trouble directing the team to one side of a boss so I could get behind the boss and shoot the glowing spot.