Sonar GTK3 theme is yet another great looking theme created by half-left. This is a GTK3 port of Sonar used by default in OpenSUSE. The theme comes with the metacity theme and the GTK2 version as well.
Download it from here
Unzip and copy to ~/.themes and use the GNOME Tweak Tool to switch theme and titlebar. To switch the theme manually, you will have to use the dconf-editor in GNOME 3