I finished it on "Veteran" level Friday. Doom3 is "OK". Great graphics, but just above average game play. Kinda like going to see StarWars EP 1 & 2. Way overhyped, building up huge expectations, but only providing basic entertainment. Nothing really special in the whole game...
In the place where you are stuck... Check every nook, desktop, shelf, around any bodies lying on the floor. Its around there. They always were....
Terror
PS. The "Cyber Demon" in the end-game was one of the easiest end bosses in the game. Hell....any game for that matter. (no pun intended).