I really like the game so far. The mechanic w/ flashlight and gun is cool, I don't see what the problem is. It just adds more tense moments. For those that don't know, Hit F to enable your flashlight, and then hit F again to go back to your weapon. This is vital!!. If you're trying to go between your guns and your flashlight w/ a mousewheel or something, you're just crazy. As for performance the best advice I can offer is: Your year old 128MB video card runs in medium quality, your 64MB card runs in low quality. Accept it. I wanted my 9700 Pro to do High so bad, but the game just isn't built that way. As far as I'm concerned, any speed complaints are from people that are trying to run it in a quality that isn't meant for their hardware.
I disagree with the poster that said Far Cry looks better. While the outdoors environments are beautiful in Far Cry, the indoor environments are only ok, and the "pink beast" models in Far Cry were just awful. Overall Doom 3 has way more atmosphere--Be that from lighting, from video screens playing in the background, or computers that you use, sparks showering down, or a fire, that has realistic smoke pouring off of it, the dust floating in your flashlight beam. Oh, did I mention the incredible animations of these creatures breaking through walls and doors, ceilings and floors?
I was very skeptical of Doom3, I sort of accepted that id would make another beautiful, shallow game, but the game has really impressed me so far.