One of the most incredibly immersive, heavily atmospheric games you can find on the market.
For me, the simplicity of the game is the key. Doom 3 stays true to its roots, making this game feel like you're playing the original Doom all over again. I liked the original Doom, so for me this is a good thing. However, I do know that there are others who will look for much more though… For example, in the Call of Duty and Medal of Honor games, you encounter unique situations like an all-sniper sequence, a vehicle sequence, or a puzzle situation. You won't find those here. In Doom 3, its just dark area after dark area filled with monsters attacking you from every corner. You just point your weapon and shoot them repeatedly until they die. Despite the seeming monotony, the concept works – Doom 3 compensates by pitting you against ambushes left and right, and giving you difficult boss fights that make you feel satisfied afterward (Especially the last one – the Cyberdemon).
The production quality is top-notch. I did not encounter a single glitch the entire game (hooray!), and I played this twice. The darkness of the areas combined with the scary sound effects (zombies grunting, lost souls screeching, eerie whispers and the dying rattles of marines all around) provide a winning combination for a great in-game atmosphere. While I thought the animations were clunky (the character models looked a bit blocky), I found the cut-scenes to be very effective (the screen zooms out from your point of view whenever entering a cut-scene, then zooms back in as you exit) in suspending the disbelief. Overall, the graphics still looks like its holding up against today's photo-realistic games (on the next generation consoles), and is certainly one of the best looking games on the Mac.
Because of the simple gameplay, the interface was very intuitive (though I found it frustrating to switch between the flashlight and the weapons all the time). The game was long enough (Around 18 hours to complete I think), but still felt interesting enough for me to play it through again.
Multiplayer mode was a disappointment though (there were no online players), but this should be expected considering the game's age. Still, if you want an intense single-player experience, make it a point to try this one out.