Imagine Ubi's Rainbow Six with incredible graphics mixed with the intensity of Criterion's Black and you'll have some idea of the thunderous experience of Modern Warfare. Yeah, it's going to be one hell of a fall for shooters.
If you are expecting to see Call of Duty 2 with some new "modern" skins, you're in for a pleasant surprise. Infinity Ward has spent the past two years improving its technology to create a far prettier game. There's an astounding level of detail in both the environments and the characters.
At one point you may step into a barn, look up and see beams of sunlight breaking in through the cracks. You'll see dust particles in the air, though that's not nearly as impressive as the smoke trail from a rocket launcher. The sun can rise or set during a level with realistic lighting effects so that the transition from dusk to dawn appears natural. There's impressive damage modeling on derelict cars; you can waste some bullets shooting out tires or toss a grenade and blow the doors off. Walk past a hill of burning trash and you'll see not only smoke, but debris floating in the air. The stunning backgrounds are actually matte paintings, just as would be used in a movie.
As for the characters, each has full self-shadowing and a level of detail never-before-seen in Call of Duty. Get close to a soldier and you can actually read the time on his watch. Once you know it's not time for bacon and eggs, you can cast your eyes on the uniform and its rich level of detail. Breathe down the neck of a U.S. Marine and you will see realistic-looking flesh. You might even see them sweat.
More impressive is that all of this works in a frantic environment. The chaos of modern warfare has AI Marines screaming ooh-rah as gunfire echoes through the ruins of a Middle Eastern city. There are explosions left and right, enemies around every corner, helicopters spinning out of control and crashing in a fiery wreck. And all of it happens at 60 frames per second. It's fair to say that what we saw of Call of Duty 4 was a greater graphical feat than Epic's Gears of War. The trailer released in April was in-game footage and not some CG magic. The screenshots posted are, in fact, exactly what the game looks like. It's not a trick; Call of Duty 4: Modern Warfare really looks that good.