"a lot of what makes certain games look impressive is the artwork and tweaking involved, not the core technology"

Couldnt have said it better myself , the Doom 3 engine is free to make you own maps and mods if you own a copy , you could literally make your own game with it , but i'm sure that most of the people using gamestudio would make low quality games with it as well , considering you just use the engine and none of the premade artwork of any kind.