Well... I beat the game tonight, playing on Normal. Overall I have to say that the single player campaign was outstanding. Every stage was full of variety and no two places looked the same. There was a nice even display of different gametypes: vehicle levels, sniper, stealth, full on commando, etc. Hell, even the glorified escort mission was fun.
The big battles were insanely intense and satisfying - some were hard and challenging while others gave you an overpowered tank and let you reign destruction freely. You even get to fly a spaceship towards the end like in Halo Reach (though your flying is way more insane in Halo 4).
The story was still a bit cryptic at times. I knew what was going on, for the most part, but there was a sense of urgency that wasn't always conveyed. And the main villain that is introduced wasn't the greatest presence - not like the Prophets in Halo 2, who loomed large over that whole game. And like Reach, not taking place on Earth felt somewhat disconnected. However, the game still has some powerful moments, and takes some fucking dark
turns towards the end. And while the end of the game isn't nearly as depressing as Halo Reach, it still hits you in the gut pretty hard.
As for the music... while it was good and sometimes really good on moments, it was really lacking compared to the Bungie games. The main Halo theme never appears, which sucks. Nor does it match the epic grandeur of Reach or of the lush richness of the ODST score. Overall it did it's job, but the music was the one thing that failed to live up to its predecessors.
Now, as for multiplayer...
I am pissed that they didn't bring back Headhunter. That was easily the most fun gametype introduced in Reach. Also, not having as straight up Free For All gametype is stupid. Dropping Firefight is an absolute sin. And I'm really bummed about Elites being removed completely as playable characters.
I also think it was a mistake to not include any Forge World maps at launch. There are three new Forge Worlds, and none of them are featured. One of Reach's best maps, The Cage, was a Forge map available on day one, and was a great showcase for Forge. Halo 4 should have done the same.
The gameplay is faster paced, but I do miss the weapon variety. With the loadout system, everyone just runs around with Battle Rifles and DMRs. Since there are no weapons on the maps anymore, Slayer matches are basically nonstop rifle matches. I still haven't played a ton of this, though, but my early impressions so far is that I like Reach's multiplayer better.
I have yet to play Spartan Ops.