Well... I've played it.
Evidently, a warez group got a hold of a copy leaked by the fellow at ATI. It was compressed and watered down and then distributed out across the web.
It is said that the graphics are not running at max.
The levels are designed to show off the engine.
It runs choppy on even high end machines.
Many sounds, textures, and models are missing.
That said....
It is the most beutiful thing I have ever seen on a computer screen.
No game released to date can even come close to the graphical quality and atmospheric sounds of this Alpha version. It still has several months of development left to go through and it can only get better.
Also, rumor has it that it has been hacked and that the map editor and multiplayer code is in the demo. If this is true, we should be seeing new maps and mods created with the DOOM III engine even before it is released.
Very cool.
P.S. - This has done nothing but fuel the flames of hype for this game. It will sell better now than it would have without the leak.
A pity it had to happen this way instead of with an official demo.