Revolutionary
First off, its online is a vast imrpovement over COD3, and COD2. Mainly because WWII is slower combat and it became repetitive faster. However, the advancement to modern times gave them a lot to work with technology wise to vary the experience. COD4 is the deepest online experience since Halo 2, level up to gain more weapons and master your weapons to earn upgrades for them. There is more than a dozen unique maps, and teh majority of them are really fun to play, the others are good, just not as good as their counterparts.
Now for the constant, the incredible campaign experience that every COD game has produced. COD 2 was said to kick it up a notch to 10, COD3 went to 11, going on those estimations of intensity Call of Duty 4 is somewhere in the area of a 56. It isn't a story driven game like Bioshock, but its fictional Mid Eastern War works well enough and it is full of those in your face, HOLY **** moments that make you wet your pants. You feel like you are playing Black Hawk Down, or in the SAS missions, Tears of the Sun. It is an adrenaline soaked cinematic feel taht no other game has ever achieved. The gameplay is perfect and there are so many moments that bring you back to your favorite movie scenes. Fight off an onslaught of attackers in a nuclear wasteland, or a city teeming with insurgents in a war ravaged Middle East city.
Now COD has always been hard, and if you want the achievements you will need to be able to tackle veteran, and I would have it no other way. I write this after becoming one of teh first people to earn 1000/1000 Gamerpoints in COD4, no easy task by any regards. Its worth it though, for the multiplayer experience and the chance to liev out your favorite movies. You can't miss Call of Duty 4.