Halo 4's campaign had the best visuals and cut scenes, but everything else was just flat. It eludes me as to why Halo 4 introduced only three new enemies, while reducing the number of Covenant foes and adding no new enemy vehicles. There was just so little variety with the Prometheans, especially because there were no vehicles associated with them. With the Covenant, you also only have three main forms with the grunts, jackals, and elites. However the Covenant had vehicles, which each played like a whole new enemy. The Prometheans had none of that. Even their weapons were nothing new (save the Incineration Cannon and the shotgun pistol).
The Prometheans also did not play well. The floating guys who threw grenades and made shields were fine, but the dogs were just annoying and uninteresting. The knights' ability to teleport was more of an annoyance than an interesting gameplay element. I'd often be shooting a knight and go "okay... and now he's going to teleport. Hopefully it's two feet away so I don't need to go on a scavenger hunt." Which is what the Prometheans were most of the time: tedious. The flying guys were exceptionally annoying to take down if you only had short to mid-range weapons like the Scatter Shot and that Promethean assault rifle, dogs would just swarm you and waste all of your ammo, and the knights felt like bullet sponges and would teleport away, only serving to delay killing them.
It got to a point where I was wanting the flood to appear, just so I wouldn't have to bother with the Prometheans. Granted the Prometheans never got to be as tedious as the flood turret forms or pure forms seen in Halo 3, but the Flood spores, carriers, and combat forms were never as tedious feeling. Replaying The Library did not feel as bad after I beat Halo 4, believe it or not.
The Cortana x Chief love thing going on was also awful, but I'd rather not go into that. I'll just say that almost all dialogue between them was cringe worthy. This is coming from someone who played Kingdom fucking Hearts without cringing.
Why remove the pro pipe and add the sticky detonator? Why not push the Promethean weapons to be more than just fancy variants of weapons already in the game? Why did the Promethean grenade suck so much? And how did that thing kill the big baddy when it can't kill anything else? /rant