CoD4's sp was great for one run through. After that it was all about the multiplayer. The beautiful maps, the awesome game modes, the wonderful 'feel' they created that balanced real-world weaponry with fun combat action, arcade-y Perks, and somehow managed to create a gameplay experience that offered a balance of stealth, sniping, MOUT combat, explosions, traps, running gun battles, territorial battles, nighttime and indoor battles, outdoor urban and rural/forest/field battles, etc.
It was one helluvan mp gaming experience, imho. I loved it. I just left after about 6 months, at which point the game - like just about every fps - degenerates into a cheatfest, whinefest, or newbfest.
I am glad I left when I did because I left on a high note, with great memories that greatly influence my desire to buy the new game. However, almost as great are the negative vibes from what they've done to eviscerate the multiplayer, which based on what has been detailed so far, appears to only shorten the lifespan of a quality mp experience for the game. But time will tell. I just know that if I am going to bother with it at all, I will need to pick it up at launch in order to be able to get the most out of the mp experience before it degenerates.