Powermetal is one of my favorite themes, definitely my favorite by Swiz. The theme is a rendition of the new aluminum used in the Powermacs and Powerbooks, and the look 'ported' to your desktop makes even my iBook look pro. The texture is perfect, and the lighted up blue widgets are professionally done, with a very 'x-serve' like look. One suggestion from myself is an option to switch to white lights, similar to the new G5's and powerbooks, perhaps through the system preferences Blue/Graphite option.
Like all of Swiz's themes, Powermetal comes loaded with extras, including several simplistic and g5 styled desktops and a safari toolbar replacement. For icons, I heartily recommend Iconfactory's TiSystem icon replacement set. It's light grey, bolted metal icons go quite well with this theme and Aluminum Alloy (another very different but great metal theme by Max Rudberg).
Powermetal is one of the most usable themes out there, and still manages to look very different from Aqua while it's at it. This is what brushed metal might become, if Apple bases it off their new metal products (just like Aqua was inspired by the iMacs I suspect).