The 3D Desktop themepack contains a whopping 63 wallpapers that range from colorful abstract images to glorious natural landscapes. If you don't find something in this themepack that pleases you, then you probably don't enjoy digital art in any form.
That said, the wallpaper collection is uneven--some wallpapers are clearly commercial ("Avatar," for example) and some are just not of great quality. No worries; after you install the themepack you can right-click your desktop, choose Personalize, and drop individual wallpapers from the Desktop Background slide show by removing the check mark on thumbnails for unwanted images.
Overall, however, the free 3D Desktop theme pack is terrific. It contains some gorgeous scenes--the mountain landscape I've selected to illustrate this review, for example--and truly amazing 3D graphic artwork. Your windows get a clear "frost" treatment that works with all of the images; your sound profile is changed to Windows' Characters; and you get the Windows Bubbles screen saver (which seems like a great choice for this Windows 7 theme).
Note: To install the 3D Desktop theme, just unzip the archive file and double-click the themepack within. Windows does the rest.