I've played Doom 3 a long time ago, but I really get what they were going for. The design choice was to make it more horror and less action. I remember that instead of switching to flashlight I rather shot in every dark corner and wasted a lot of ammo.
Some missions are even built around flashlight. For example the one where you are escorting the robot. He has flashlight and lights enemies.
There are also more design choices that support horror aspect of the game. You are slower. Computers in the game are real time if I remember correctly. That's also a neat little thing.