What the hell is this game? Doom was about super fast run-and-gun action, killing demons by the truckload in mostly well lit environments. Here, you're just running around with a flashlight in pitch black hallways and rooms like a dumbass. Yep. Carmack thought this was a good idea for Doom 3. Open some doors and get randomly pounced on. Step into a room and hear an enemy, but now you gotta make the decision of either having your flashlight out or a gun. Oh, and don't forgot all the audio logs and emails you'll have to go through to get some random door code or box code. 10/10 Doom gameplay, John. So impressive...
Now, I didn't really get the proper way to play this game either until I came across this
quite awesome video of a Nightmare speedrun for Doom 3. And then it hit me. You see, this game is the opposite of FC2 in a way, and the way John Carmack intended everyone to play Doom 3 (creeping along corridors with the flashlight) was kinda shit. When you don't take your time, and you just blast through the areas as fast as possible, the game instantly becomes MUCH more fun and what Doom 3 was supposed to be. It's still not perfect, but it does offer a much more different and unique experience. The weapons are mostly well-balanced for this as well and quite satisfying.
What I recommend is getting a handy list of all the door codes and etc. so you don't have to look through all the damn PDAs. Having said all that though, I would be lying if I said I didn't enjoy Doom 3's more immersive atmosphere. I guess I would also recommend just playing the game normally if it's your first time, and if you find it's just not working out for you, then switch to a much quicker more intensive play-style.