I think the GUI is interesting and innovative. I do think it should perhaps be collapsible to a smaller circle or at least have a short cut key to toggle 'Hide/Show menues' so you can quickly toggle them invisible if needed. If not already considered then shortcut keys are cool as well.

Martin (MB) had this project in Showcase last year. http://www.superfluxus.de/tm_00.jpg The circle in the bottom left pops open and closed the menu.

A small thing I might consider would be either change the small submenu from a circle to a bar or make sure you have animated button states on hover over the X and icons. Otherwise I think people working quickly may frequently click the X instead of the icon as it is 'near' all icons.

Other than that when you have different icons, matching colors for main menu and its submenu and perhaps a title for stuff on the big wheel 'Material Tools' etc it will help people get use to the interface. For me it works. Reminds me a little of Eovia's stuff and even an artist pallete.