Atmospheric single-player experience which you will remember for a long time.
At first sight, Doom 3 is just a regular old school "shoot-em all" sci-fi FPS. But the certain of its features truly set it apart.
First, Doom 3 is hands down the best looking game today, additionally with superb positional audio, that nonetheless doesn't suffer from slow frame-rates and long loading times. This allowed the designers to create a truly immersive environment. Usage of predominantly dark areas combined with the amazing dynamic per-pixel lighting and the generally gruesome work left by your hellish opponents all around the base creates a wonderfully tense atmosphere for the player ... who forced to choose between wielding a weapon or using a flash-light is constantly either unable to quickly defend himself or see danger approaching. This combination leaves you advancing cautiously, listening to the ominous ambient sound of the game, footsteps, growls, hissings, always on edge where will the next attack come from.
All the monsters are designed in amazing detail, be they the weakly imp or a mighty hell-knight. You will get plenty of visual thrills from every encounter. The game also introduces many of the monsters in memorable cut-scenes usually making use of the game's physics engine. The first pinky you meet beats his way through the railing above you then starts breaking through metal doors into your room before it finally jumps through the window, quickly closing in on you for melee. Scenes like this or your first encounter with a hell-knight who tosses a scientist wearing environmental suit like a rag-doll before attacking you are sure to leave you with goose-bumps wanting for more.
The base also feels incredibly life-like. Before the hellish invasion, you will walk though a complex functioning research center, full of scientists, maintenance personel and administrative clerks. After the invasion, you will often find audio logs or emails of the former staff divulging you every day details of the facility's final moments.
The storyline is advanced by these means as well. You will slowly learn what exactly happened to the ill-fated research center as well as the fate of another two investigators send there, Eliott Swann and Jack Campbell.
I had only two problems with Doom 3. First, the difficulty is rather low. This is however a problem only in hindsight. While playing the game you are constantly on edge, scared of who will attack you next, always afraid to expend ammo for valuable weapons, conserving it for just those special close encounters with hell-knights. But looking back, there was never really a shortage of ammo and medical supplies, it's just the game's spooky atmosphere that made it feel that way. Still, I wouldn't have minded if the game was a bit harder, especially after you get the soulcube which is able to kill every (non-boss) monster in a single shot and replenishes your health to boot.
The second shortcoming of Doom, and the more severe one, is that the game seriously loses steam in its second half. The first part of the game has so much events packed to it as well as watching the progress Swann and Campbell are making that it leaves the second half empty in comparison. Important events advancing the story line are much more rare later in the game. I would have loved to know what happened to the two in the Delta Labs, for example, alas you are left ignorant. Additionally, by the game's final half the horror element wears out. This is caused chiefly by learning the tactics used by each monster so you are able to quickly determine just by sound what kind of an enemy approaches, what weapon to equip and how to duck, The game then boils down to a simple shooter ... simple, wonderful looking and sounding shooter nonetheless.
Bottom line: an amazing game that should be played by anyone interested in action games, horror or the state of the art of graphics technology.