The shaded brown theme is similar to the Zune software colors. Imagine that. If you have not seen the Zune software, click on the thumbnail for a larger view. As you can see, the overall look and feel is pretty dark. I prefer dark colors although I think many of us are used to white backgrounds with black text. A dark background with lightly colored text is a welcome break for my eyes.
The downloadable theme only themes the borders, task bar, start menu, etc. for Windows XP programs. If you want to further alter operating system background and foreground colors, go for it.
Oh, and for you Halo 3 fans, the picture of Master Chief on bungie.net matches the Zune theme very nicely. Coincidence?