One of the few GDC's I went to I saw Michael Abrash's lecture on the Quake engine and its potentially visible sets. One thing that struck me the most about that lecture was how much he talked about lighting and how important it was at Id to have dramatic lighting.
Doom 3 shows just how seriously they take lighting. Flickering lights, moving lights, colored lights, all casting dark, high contrast shadows all over the place. And, of course, your flashlight. This time, they made the lighting a part of gameplay. You can have your flashlight out - you can have your gun out - you can't have both at the same time. Some people have been saying that Doom 3 isn't that innovative; well, this is an innovation. A small innovation, perhaps, but an innovation nonetheless. And a risky one! With so many wankers out there saying "I just want to frag shit", telling them that they're going to have to do their fragging in the dark might not go over well. (And with some people it didn't - as I understand it, the "duct tape" mod - where your flashlight was attached to your gun - hit the streets within days after the release of the game.) It's the sort of innovation that your publisher will quash right away. You see, if you're going to have some areas of your game require a flashlight, you have to make those areas dark. So dark that no matter how much the player turns up the brightness on the monitor, they still can't see anything. And if you make your areas that dark, your publisher is going to say to you, "What's the point of your state-of-the-art renderer if you're just rendering a black screen?"
But it works. For me, anyway. The truth is most of the game is lit enough that you can shoot just fine - those few areas which are pitch dark and you have to switch between flashlight and gun are rare, but those areas are scary and intense and interesting. After playing long enough I become confident enough in my abilities that I was willing to have the flashlight up all the time; if a monster showed up I knew I'd have enough time to drop the flashlight and still get enough rounds in it to kill it before it hit me. (And if I didn't, well, there's always quicksave.)
Doom had a few scary moments: some atmospheric lighting, something jumping out at you. But Doom 3 is all scary all the time, this constant tension. If that's what you're in the mood for, nobody does it better.
Side note: at first, I was scared to go in elevators. If I was designing this game, I thought, I'd put something scary in here. The monster would come through the door right as it was sliding shut, a la Aliens. After a while I realized I never got attacked in elevators - they became my safe haven to reload all my weapons while I changed floors. Which again brought to mind Aliens, the scene where Ripley is arming herself as she goes into the nest. Dramatic either way, really, eh?
It seems Id has learned some lessons from Valve. One of the lessons: create the illusion of a continuous world. As you go from level to level in Doom 3 you can imagine how they're connected. Once you even revisit the same level. Another lesson: immerse the player in the story. On the face of it, Half-Life didn't tell a story much different from Doom's; in both games, science has unlocked a gate to evil and you're the guy who has to go in and deal with it. One of the things that makes Half-Life great is the way the story is told: in the quality of the scripted events, the interactions with people, the convincing details, all without a single cutscene. Doom 3 has caught up to Half-Life in this regard: it tells the same story as Doom, but tells it the Half-Life way - although there are a few cutscenes, to introduce bosses, most of the story develops while you're playing.
Rookie game designers think that the more types of enemies a game has, the better. Doom proves this isn't true: what Doom and Doom 3 gives you is a small number (I haven't counted, but it's probably around a dozen) of enemies, but they are highly differentiated. I had a different favorite tactic with each. Dodge imps fireballs while hitting them with the shotgun; use the machine gun on the tiny spiders; plasma gun for the skeletal things that shoot the missiles; rocket launcher on the giant floating head things; etcetera. If a game has too many different opponent types, they're going to start feeling all the same, except possibly with more hitpoints. This is a place where Doom shows its ancestry to classic videogames; more and more games these days have lots of enemies with only cosmetic differentiation. A step away from gamism towards simulationism, I suppose, so not necessarily a bad thing, but you do lose that pure-game pleasure.
And those are my notes. It's midnight on Thanksgiving Day and I'm going to try Half-Life 2 now.