It runs about like a dachshund in knee-deep mud on my machine, so I turn the graphics down as low as possible on a smallish screen and I can get playable frame rates. Playing online with Hex and Soapy with Soapy hosting, I would occasionally dip down into the low-teens for framerates, but it still played alright and I had a lot of fun. It is taking some of getting used to without the dodging and shield gun. I'm really missing both of those quite a bit, but it does feel like the original UT more than 2k3 or 2k4, except with vehicles and a hoverboard.
I'm not looking to upgrade much of anything on my PC any time soon, but I look forward to the day I can run UT3 with full eyecandy.
