Having played through much of this now, I have to say, the visuals are nothing short of astounding. I have found that some of the lighting is not actually dynamic, but this does not bother me. Point is, artistically and visually it looks gorgeous and that's what counts. The art, architectural design/complexity, general look and feel etc are all beautiful to behold.
It looks cleaner than past Halo's, and above all, I think the biggest difference is in the lighting and post processing. I said earlier based on vids and screens its adopted some Killzone esque appeal and I still stand by that. The flares, iluminosity of lights and bulbs, smoke, sparks, effects etc. Only the art style is different, it's like a mix of Halo, Mass Effect, Rage and God of War. More smooth with a hint of a painterly like aesthetic.
Only things this game is really missing visually that would have closed the deal are motion blur and SSAO, which I do feel is missed, since at times the lack of those little snippets of edge shadowing or contrast can make certain scenes look a bit garish and samey. SSAO would have just given it that slight extra pop and made cluttered architectural elements stand out more realistically.
Other that that though, this is most definitely one of the best looking games this gen. In the top 5 for sure.