GNOME-Shell or Unity: whichever desktop shell you choose chances are your favourite GTK+ theme will need to update to take advantage of the new features and elements offered by both.
The following GNOME Shell by deviant artist ~half-left should placate the brooding elementary fans amongst you worried about the switch to Shell.
Download and install
Full instructions on downloading and install theme can be found on the DeviantArt page @ half-left.deviantart.com/art/GNOME-Shell-Elementary-Git-193232931
Do note that the theme is for use with GNOME Shell 2.91.x. or higher.