I kind of summarized the interesting points in the IGN preview.
No multiple protagonists, story follows one playable character (and his brother)
US was ravaged by a "mass event" (not WWIII)
Completely new conflict (no Modern Warfare ties)
The use of Ghost's mask is pure fan service according to IW
Done with cliche Russian "threat"; players face "resource rich" states (oil abundant South American nations)
IGN demo shows "No Man's Land" level (San Diego, desolate wasteland, destroyed infrastructure)
No Man's Land emphasizes stealth; player must navigate contested terrain
One area has you taking out enemies in gas masks+hazmat suits surveying several mile-wide crater
Covert combat was distinctly reminiscent of "All Ghillied Up (COD4)
Your service dog accompanies you
More than just an AI companion, it's a remote recon scout
Can be controlled via a tablet-like viewfinder (based off real life Navy Seals)
In the real-world field, SEALS outfit highly trained dogs with periscope-like camera and specialized earpiece; allows team to see/hear everything dog does
You can control the dog in-game; can lunge at enemy's throats
You can bark to lure enemies into view
Second demo
Underwater level
Actual battles take place underwater
Enemy divers submerge from above from boats
Underwater assault rifle (real life Russian APS rifle)
Intimate use of cover underwater, behind rocks and reefs
Verticality in the level; get an elevated shot or dodge
Enemy subs use sonar blasts which cause damage to the player and cause tremors in the environment
Player must swim from cover to cover
Destroy the enemy sub with portable torpedo-