When you reason like that, since the first polygon was rendered, everything else has been 'done before' somehow...
Obviously there was some very nice shaders and detail going on there, that you definatly will not find in Half-Life 2 today!
But, that said, I think the MGS4 clip was very impressive technologically, but
mainly on the artistical aspect. Many polygons and nice texture effects are possibly anywhere on each platform now. But applying them in the nicest way possible,
thats the art of game development and truly impressive graphics. And Kojima's team sure did nail that in the MGS4 clip. Now it's waiting on how the gameplay will turn out, and if it will achieve that level of realism as seen in the clip.