With Bungie leaving Halo development, 343 had the job of not destroying the epic franchise that is Halo. They didn't, and they created an almost perfect all-around FPS. The co-op campaign is one of the best around, spartan ops is a decent short story co-op distraction, and the online play is fast paced and as fun as ever.
The campaign focuses on Master Chief and Cortanas story together, and to not create a spoiler, I'll just say that it's amazing. Introducing a new species creates a blank slate to go off, and it also gives Master Chief a ton of new enemies to dispose of and new weapons to master. The graphics are the best I've seen on a console to date, and Halo 4 boasts some truly unreal music & sound. Each gun sounds powerful and unique.
Spartan Ops is my only complaint to Halo 4. Halo Reach was simply epic, and I'm sad to say that 343 nixed the Firefight altogether. No more waves of enemies, instead you have a Spec Ops type mode where you play short stories solo or co-op. They are linear and always end up with you killing x amount of guys, so these will get stale for me really quick. Once the first 5 episodes are done, I don't see myself replaying these.
Online multiplayer is where it's at though. 343 created a more fast paced sharp experience. Everyone has sprint, not just as an ability, so that changes things right there. There are a ton of new perks, powerups, in-game weapon drops, and a new arsenal of weapons to use. Both enemy and Spartan weapons can be used. And if you score a few kills, you can deploy weapon/powerup drops to help with killing the other team. Big team battles are awesome, and the tighter maps are just a ton of fun.
All in all, Halo 4 does not dissapoint in any area except the other co-op modes. But with the best Halo campaign to date and another amazing online experience, you don't need any co-op modes to compliment the already super deep gaming experience. A must buy.