If you find the ratings too limited in iTunes and would like to be able to give half-star ranking, such as 4½/5, then you can enable this tweak.
Start a new Terminal session (in Finder click Applications > Utilities > Terminal).
To enable this setting, type (or copy and paste) the following command:
defaults write com.apple.iTunes allow-half-stars -boolean true
To reset this setting to the default value, type (or copy and paste) the following command:
defaults delete com.apple.iTunes allow-half-stars
To activate this tweak please close all instances of iTunes, or wait until the next reboot.
Close the Terminal session by typing
exit at the prompt.
Disclaimer: Making any changes to your system can cause serious problems that may require you to reinstall your operating system. We cannot guarantee that problems resulting from these modifications can be resolved. Please follow the instructions carefully and use the information provided at your own risk.