I don't care about any of the characters except for Chief, Cortana and Buck. I know Chief's teammates but the only reason I do is because I read the novels. There are 15 missions, they feel like the bare minimum for level design. Over saturation with the vehicles (I didn't think there was too much of a good thing in Halo but there were with vehicles in this one).
Also, there are about 3 full levels you play Chief. Mind you, that's the character I wanted to play as for the WHOLE game. I counted five different encounters with Warden Eternal. Each fight stays the same with mechanics until the second to last level of the game where there are about 3 (maybe 5?) Wardens. The game lacks absolute polish too. On heroic some AI were poor and stuck somewhere in the level and couldn't fight because of a constant running animations until I put them down. The game doesn't take time to setup Locke, his team, Chief's comrades, how Cortana came back from H4 or the last stages before her transition to rampancy. Cortana becoming evil and starting an AI uprise is great on paper but horrible execution. The third act seemed like good action sequences and left open enough for H6 but the build up to that point was underdeveloped. Some of the mechanics I didn't even release were available until I accidentally did that button combo near the end of the game.
I'd give the campaign's story about 4.2 out of 10. I love the new version of guilty spark (I forgot her name but her personality is great). The story didn't go as expected either after what I remember from the advertising for H5.
I haven't played the multiplayer and it could play well but turned off enough from the campaign.
Overall score 5/10