As for Doom III and HL2, it's not an OpenGL vs DX9 thing, I agree Doom III has highly detailed facial expressions and awsome lighting and shading techiniques, but that's it! I mean, if you compare it to let's say FarCry, you'll find out that FarCry's textures look far more detailed, I really wonder why they didn't implement highly detailed textures in Doom III, the textures look really poor in most of the places, maybe they took advantage of the darkness and shinyness of objects in the game and thought nobody would notice low texture details, here are some pics that describe what I mean, you can never find such texture bluriness in FarCry:
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These are just examples.
I am not attacking Doom III here, I love this game and the graphics are nice, but it really annoyes me how ID didn't put detailed textures in a 2004 title that was supposed to revolutionize first-person shooter games on PC.
By the way, I am running Doom III on 1024x768 Ultra Quality 2xAA. And I wasn't zooming on those pics.