IGN hack Jeff Haynes has been to Konami in Japan and finished MGS4. As you can see here, in a piece entitled, "I'm the first American in the world to have beaten MGS4, which is freaking awesome," Jeff's pleased by this.
You should read all of this, but a stand-out bit says that the game's far more open than previous instalments.
"Whereas previous Metal Gear Solid games have been relatively linear in their approach, MGS4 is much more of an open-world affair," said Haynes. "While there are still specific locations that Snake will need to get to (which will constantly be indicated on Snake's mini-map), the environments that he finds himself in will provide multiple paths to get him to his eventual destination. This provides much more flexibility in how you fight your way through the battlefields that engulf MGS4."
In case you missed it, check out IGN's interview with Kojima as well. Next up: news that IGN's having Konami's love-child.