I love this! A great example of post-Evangelion skinny mech design! I see bits of mortar headd, a bit of Zaku in the face, and Zone of the Enders here and there. The only odd thing I can think off is the knee joint, the smoothness isn't reflected anywhere else. The gradient is a great touch.
It's a manga series by Mamoru Nagano, but an OVA exists out there (it's an overview of the first few chapters in Five Star Stories). I recommend reading the series anyway, as there's much to delve through--not to mention the amazing mecha designs.