Honestly, this game doesn't look any better than all the X360 games at all. The Ruliweb images show quite lowpoly models, enviroments and low-res textures, some are actually looking too bad even for COD2. Contrast is pretty low, too, giving the images a wahsed out look.
Gameplay might end up cool but it certainly won't be the nicest game on the PS3 or in the next gen...
It's about the total package. MGS series are known for their direction and atmosphere. You can pick any old FPS and it might have better rendered graphics, but the plot, cinematics, camera angles, music, and other things combine to make the MGS series a favorite. ID's games show you how leading edge engines can still lead to a dry user experience.
I mean, really, what other game has half-mechanical half-BOVINE? tanks walking around? Even if you don't think those cow-tanks are as detailed as enemies in Lair or GOW or other titles, they are far more exciting to watch in movement IMHO than what I've seen in other game trailers and the n'th spider/tripod alien.
MGS4 may not be the game with the best rasterization of PS3 games, but when you combine direction, music, plot, atmosphere, game play, enemy design, cinematics, it will outclass many games designed purely with a focus on rasterization quality.
(I tried to not mention specifics for comparison, alas, I need alteast one or two concrete examples. I'm also not sure why Laa-Yosh needs to bring up XB360 at all. I mean, from a GPU point of view, I would expect Laa-Yosh to assume rendering capabilities will be on par between the consoles)