It's really itchy to have menu list cover half of your screen, they're way too biggggg!!!
I've googled to find the solution but it's like impossible @@!
Finally, I got the answer. This is how-to make it better look for you.
Choose a theme to use in order to edit that theme, example, I use 'Is Ora Smooth'.
Then I locate to its settings at: /usr/share/themes/Is Ora Smooth/gtk-2.0/gtkrc
Run gEdit or any text editor under root permission to edit this file.
Add this option into the file:
gtk-icon-sizes = "panel-menu=16,16"
I'm not sure if you want to make it smaller but the size is often like 16, 24 or 32.
Choose the one that best fits for you.
Logout and apply that theme, you'll see how beautiful it is!