I don't think there is any beauty in modern flat themes but it is the modern way. Here is my attempt to add some interest.
I don't use Ubuntu so I have no idea if this will work for anyone. It works on my Sabayon box where I have a mix of mate and gnome 3 elements.
The link has Gtk2, Gtk3 and metacity themes.
Please can someone try it and amd comment to let me know if it works, thanks.
Please be aware so as not to waste your time. From a comment below it is clear the theme does not work in the latest version of Ubuntu.