I'm on a 2.4Ghz, Radeon 9700Pro, 1G RAM. Running at 800x600 Medium Quality. It's both stunning and almost always 30fps (with an occasional blip below, but always very playable). I'm curious to try higher res + higher quality just to see what it looks like, but I believe I'm at the edge of my machine's capabilities currently.

This game is so incredibly immersive. The amount of detail is just amazing in the environments -- it's obvious why it took them so long to finish it. The other part that is very surprising is that there really is a story and it is actually interesting. They also have tons of unique NPC's -- no repeating Half-Life scientists ("I won't move another step!") and the voice acting is great. Definitely some serious attention to detail here.

By the way, I'm at the forum here because Doom just made my adrenaline shoot through the roof and I need to come down. It's a really creepy game.