Campaign/Story review
The story has its moments with climatic high points and new conflicts that are all done exceptionally well. The lore of Halo's universe has become some-what convoluted but the plot revolving Chief's humanity and Cortana's vulnerability both give substance to Halo 4's campaign and venture into areas not explored in previous games.
There are some areas that are lacking, Requiem in particular doesn't have the impact it should and often you may forget you're inside a giant hollow planet. Even though the plot between Chief and Cortana is great I feel much of Halo 4's design was simply to get the ball rolling, I expect Halo 5 & 6 is where the meat of this trilogy will be.
With Halo 4 resolving certain issues the path is now clear for the story to really open up.
Gameplay
It doesn't feel entirely like a Halo game. It has the Chief with some familiar enemies and weapons but overall it does departure from where Halo 3 left off. It is good, but different.
The Prometheans are far more interesting than the Storm Covenant, but lack diversity. There are different classes of Promethean Knights but they are all too similar in design to notice the difference from afar. The Watchers and Crawlers are not as "cool" as the Knights but complicate the situation and empower the Knights further. The Prometheans do bring a new level of challenge to Halo and I feel will be welcomed.
The A.I. may come as disappointing at times, mainly from the storm Covenant. Elites feel lifeless and stiff, rarely do they pursue you, and the taste of repetition sours the experience.
Graphics/Art
The graphics are a huge step up and make this one beautiful Halo game. There are a few levels where the vistas are large and open but I felt Halo 4 is much more claustrophobic compared to previous games. It is by no means a corridor shooter but definitely more confined.
Closing
For Halo veterans there is something there for you in the campaign, and I feel the next 2 games will vastly expand on Chief's humanity and open up more story arcs. Truly the possibilities are endless.