Kojima is typically self-deprecating, despite MGS4's epic sweep. He describes his original vision for the game as a '10', which was scaled back to a '1' - after basing his original concept on a hopelessly optimistic estimate of (the then unfinished) PS3's power; revising his ideas when he saw the finished tech specs.
He is at pains, however, to stress he's impressed by PS3, and feels MGS4 pushes the limits of the Cell chip. In the very first teaser trailer shown at E3 2005 (rendered in the MGS3 engine on PS2) where Snake plays musical chairs, the theme was 'Nowhere to Hide', with the implication that MGS4 would have a completely destructible battlefield.
After looking at PS3, Kojima realised this wasn't possible, so the finished game looks 'merely' as good as, say, Uncharted or GTAIV, though you can't destroy everything. At times, it's a hi-res version of MGS3, at others, the most cinematic, improbably-beautiful, game in history. One chaotic real-time scene caused us to scrawl 'THIS IS NEXT-GEN!!!' on our notepad, for no reason than we had to tell someone.