Before getting to deep into this, I want to make it clear that I am not an artist, but a musician. What I like most about this work is the detail on the nose, specifically the imperfection of his face; this and the tension in the face and neck very much reflect the guilty anger of Tennant's take on the Doctor. The image of the Doctor in front of Cybermen, lets face it, has been done a million times, and while I love the posture you've given him, the limits of the chosen subject prevent any really great vision from being realized. While I say these things about the chosen subject, I am extremely impressed by how you executed. The shading and shine on the Cybermen is absolutely stunning, and the details of the face neck and figure of David is superbly done and reflect his time as the Doctor.
I'm starting to grow a real appreciation for how straightforward your compositions are but still so exciting for viewing.
There's a feel on his face where when I cover different parts with my finger, the eyes and nose don't quite have that lifelike feeling as the rest of it. Your craftsmanship is admirable and I hope you don't get annoyed or mind when I point things out.