Powder is a variation on the traditional fight yard arena. Snowfall lowers visibility, and players can jump between rooftops.
Powder is a map I made on an impulse. After I started making TF2 maps I remembered back to when I made Mountainside, and I realized I should put my snowy theme in a playable map. I worked on Powder as a side project.
The map isn't completely practical for the CS:S community, because typical players of fy maps don't want to sit through a long download. But I'm glad I made the map, because it's rare to have an fy map with extensive detailing.
The layout isn't too special - it is a variation on the popular "fy_iceworld" layout. But jumping on the rooftops is fun, and makes it a good map for 1v1.