Wow...I was sincerely disappointed by this demo. I've got a quite good (Athlon XP 2800+, 1GB Corsair DCDDR, R9700 Pro) gaming machine, but even dropping the detail at 1024x768 didn't result in a playable framerate. The HL2 leak looked and played a lot better than this, and it's months from being finished, and this is the demo they're choosing to release to help sales of DX2? The console feel is pervasive; I had hoped they'd make a good PC version and dumb it down for consoles, but instead they're taking the poor-quality console version and selling it to PC users with little improvement.
Have to agree on all points there, this was a real shock. Even as a multi-platform gamer I'm shocked at what they've done to this - it's horrible to play on a PC.
My biggest gripe is the terrible performance on top notch hardware, which is very disappointing. It's made me very worried about Thief 3, which I was looking forward to a lot more than this.