Windows does not give much option to customize your operating system’s feel, other than its wallpaper and aero theme color. If you try to install a custom theme, which is not signed by Microsoft, it won’t run that theme. Microsoft restricted the use of custom themes on the basis of security.
But if you wish to install such custom themes, you can patch the system files and remove the restrictions imposed by Microsoft. Manually replacing the system file is not advised as it may lead to system instability if done wrong.
There are many patches available online that can patch the system files with just one click of the button, but not many are available for Windows 8 just yet.
If you are looking for a patch that will work on Windows 8, then try UltraUxthemePatcher. It currently supports all Windows operating systems, starting from Windows XP to Windows 8.
UltraUXThemePatcher Setup Window
To patch the system files, run the downloaded file, go through the simple setup procedure.
Patched Windows 8 RTM running Windows 8 RP Theme (w/ Aero Glass)
If you wish to install the same theme as mine (from the above screenshot), please download it from here. If you want to try it with aero glass, go here.