Doom3 is a slightly different FPS in my opinion. If you have played all time classics such as Half Life 2, you will appreciate the difference here. It's a kind of mix between previous Doom games and Resident Evil 4. It's all about atmosphere, and especially in the first hours of the game you will be freaked out. The game tends to be relatively classic in terms of targets (get PDA of person XX to open door A, etc.), but will keep you glued because even though it's been released in 2004, it's still looking great!
Other reviewers stated you need a monster of a PC, but I disagree especially by today's standards. If your PC is 2 years old and has a graphics card from that same time, you are fine to play the game at maximum resolutions and details. My PC is from last year and was mid-range then, I can run the game fine at 60fps with all at maximum (ok, I have a X1950XTX, I admit). When it was released, yes it was a PC killer, now, it's a great looking game with average requirements.