343 Industries really caught the ball on this one. Campaign was excellent, Spartan Ops and War Games are both very entertaining. 8/10 from me. It would be higher, except I was slightly disappointed with Forge (I'm an avid forger, and created 100s of maps in Reach). There are three dedicated Forge maps, but I still feel let down by the lack of size and freedom that I was looking forward too, and that I experienced in Forge World in Halo reach. Some points (good/neutral and bad);
Halo 4 really showed Xbox 360's relatively primitive processing capability with Forge. Placing objects and then re-entering Spartan mode takes time, a few seconds to load the lighting and shadow of the object(s).
There is still a limit to the amount of a type of object you can place (100 blocks, 100 walls, 100 decorations, etc).
Momentum is not conserved when entering Spartan mode when moving fast in Forge Mode.
There are no UNSC air vehicles at all (in Forge), the only flying vehicle being the banshee. I do not understand the reasoning behind this.
Mass-deletion of objects is much easier.
With all that said, I am still having fun creating new maps with the variety of forge maps available. It will still offer great customisability, but a few little things could make it a lot better IMO.