1.) Single player campaign will be a lot more "cinematic" this time around.
2.) Enviroments will be
much larger. 4 to 5 times larger than some of the biggest single player maps from the original, to be more specific. And no repetitive areas or combat situations
3.) Bigger focus on vehicles. A.I. Marines will now be able to pick
you up and drive you around the maps. You can not only hijack an enemy's vehicle, but they can do the same to you. Vehicles with weakpoints and area specific damage. And, well... There'll be more available to you.
4.) A.I. of the enemy and Marines will work much better with and against you this time around. Marines will look out for eachother, watching out for snipers, taking cover when needed, providing anti-air with heavy weapons. The enemy will co-ordinate as a team very well too. They will hunt you down if you go missing(even using flashlights in the shadows), scale walls and duck under logs,
BLAST through scenery(Hunters...
) if necessary to defeat you. And also, there's stuff like this:
Can't use the same tactics as in HALO 1.
... What I miss? :l