COD4Forums.com have posted some quotes from a magazine that describes new aspects of the COD4 multiplayer game modes.
Here is what to expect:
"- In multiplayer, you get experience points for your persistent character stats. A kill gets you 2 points, a headshot gets you 3 and an assist (wound them but someone else kills them) 1. You'll unlock new ranks, skins for your character and new weapons. The system is implemented so they add can additional unlocks that come with patches.
- In both single and multiplayer there are hardpoints. Points on the map that give you a specific advantage over the enemy. An example that was given: A radio that calls in an airstrike, capture it and a helicopter will appear and attack the enemy with its rockets and machineguns.
After the attack the hard point goes neutral again.
- A new gametype, Realism-Mode. Grant Collier says the mod community had implemented this into the previous titles and now they'll add one themselves. In this realism mode you die from one shot.
- There will be vehicles in singleplayer, but not in multiplayer."