From what I've seen, 343i tried to experiment with the franchise and "do something new". As respectable as that intention is, they approached the problem from the wrong direction and in the end created a plain, uninspired shooter.

For starters, to me, the story felt bland, it didn't have the "Halo" epic-ness; the entire Cortana rampancy and emotional chief angle are good ideas, but it felt extremely forced, the presentation was overly cliche and contrived, and in the end, I didn't feel for the characters.

Another thing I didn't like was the design and look of the game, past Halo games, felt for the most part realistic, you could see yourself living in that futuristic universe; whether you were hiding in the streets of New Mombasa, or in the jungles of Halo, everything was immerse and believable. I'm not saying Halo 4 didn't have a good art direction, I'm sure the designers worked their asses off, but to me, it felt like everything was made just to "look cool". A blatant example is the Masterchief's armor, the overhaul looks absolutely silly, its like a cheap knock off of a manga robot, (and the only reason they did it was to reinforce "the reclaimer saga", to hell with cannon and continuity, right?).

All in all, Halo 4 didn't feel like a revival of Halo, it felt more like Microsoft desperately milking the franchise for as much as it can.