I've always found the dark side of the Doctor's personality really intriguing. For a guy that is so wonderfully silly and kind, there is also something dangerous and unsettling beneath the surface. I think that side was always there but it really comes into play during his seventh regeneration. I think at that point in his life he has known so much loss and it shows. I think that the way his personality progresses through his regenerations is fascinating.
Trying out some new art techniques as well. I enjoy this style and might develop it further... Let me know what you think.