Based on lassekongo83's Zukitwo.
Using some code from the default gnome shell theme
GNOME Shell 3.6 compatible
A simplistic theme for gnome shell
Pretty much monochromatic, no rounded corners, no gradients.
Looking at it now, some might consider it a bit Metro-ish, but that wasn't the intention - I started off from Zukitwo thinking that the blue gradient-ish highlights it uses were a little ugly.
I might make a variation at some point with the same flat monochromes but rounded corners.
Several options for close-window icons and switches are included. I don't think these are quite right yet. They're very simplistic icons if anyone wants to try to improve them.
Checkboxes aren't done in the right style, but they don't pop up very much in shell, so I haven't bothered to create my own SVGs.
Looking Glass and the keyboard aren't really in style yet. I don't use the on screen keyboard, so don't know what it looks like.
I have the opacity of popup menus and notifications at 0.9, you may wish to change this (default shell is 0.8)
Finally got round to uploading my 3.6 update. I started again from Adwaita so it may look a little different, but the general style is the same.