I have few theories, honestly I am disappointed by the quality of screenshots, one year ago Half-Life 2 seems out of this world, but now it doesn't look extraordinary just look at the shot of railway track, of course you cannot judge the game by screenshots, so I am only commenting on graphics quality, some reasons:
a) Screenshots taken at low details and without FSAA (Why would Valve do that? Usually in previews you see best quality).
b) They are also targetting for XBox, and this is how game is supposed to look on XBox.
c) Scenes are too realistic, like we see in real world and therefore they don't look extraordinary (may be it is too far fetch).
d) It is THE best quality of Half-Life 2 in terms of graphics (if this is the case then I am disappointed, but surely gameplay will be much better then any other game).
a) Screenshots taken at low details and without FSAA (Why would Valve do that? Usually in previews you see best quality).
b) They are also targetting for XBox, and this is how game is supposed to look on XBox.
c) Scenes are too realistic, like we see in real world and therefore they don't look extraordinary (may be it is too far fetch).
d) It is THE best quality of Half-Life 2 in terms of graphics (if this is the case then I am disappointed, but surely gameplay will be much better then any other game).