It's a reskin. Admittedly a very attractive one (visually and aurally). But there's nothing new in the combat or the weapons. The promethean weapons are hardly anything interesting (light-rifle is weird mix of the battle rifle and the Cov Carbine, suppresor is the assault rifle, etc.) and the grenades are highly unsatisfying.
The story is nicely written and well told. But honestly, just make a movie, guys. If you want to grab me by the balls you have to make the game as satisfying as the other Halo games (which have less flash and more substance), and add new elements that provide more of a challenge, and more room for novelty.