Looks like the graphics got ramped up for release!!!
Also, here is a pretty nice trailer. It is in japanese, but still nice to look at.
Gametrailers.com - MGS4: Guns of the Patriots - Japanese Story Trailer
Also, someone posted this on a different forum. You can tell the overall change is pretty amazing. Before everything seems lighter, fluffier, and soft. Now it has darker tones and I personally think it looks a lot more realistic. It also seems now, the draw distance is a lot farther. It doesn't get as blurry farther away.
Overall, I think the surroundings are better. I also think character details is greater now too, except for Snake's and Otacon's face. They looked more realistic in the earliest trailer. Still look good now. He has more wrinkles!
Either way, the screens are bad quality. Just watch the video