This is a textbook example of well-thought out compositional elements, light and color. Although the color palette is limited by the subject matter, the variation of hues really make this painting pop. The use of overgrowth as "hair" to frame the wooden face was perfect. The brushwork is very adept and adds a tremendous amount of character to the composition. I did not see a mention of what program was used to render the image (Photoshop, Painter, ArtRage, etc.) but I'd be curious to know what program was used and what brushes. I liked the fact that the artist included WIPs of the work--this would make a wonderful tutorial. Great job!
First and foremost... FANTASTIC WORK! There is not much to say about this piece. As a digital painting it looks great. As a piece of fantasy art, it looks great.
As for the ratings:
Vision: Perfect, I think you accomplished what you wanted. A living tree.
Originality: Not bad. The piece looks wonderful, but I have seen this image in one way or another several times. But who cares! We all love to recreate things we see. It's what artist do.
Technique: It's solid. Your structure and build of the piece is spot on perfect. Digital paintings get away with many flaws because it looks cool. My art teachers might rip you a new one but at the same time praise you for letting certain details go to concentrate on others.
Impact: Eye catching! From first glance I wanted to look more at the piece and find out about the artist. This makes other artists want to try it or just draw something. Inspiring.
I don't feel qualified to give a full critique, but going off of what Kalilak11 said, I agree that the blankness of eyes when I want to be drawn to them is rather incongruous. On the other hand, giving her eyes proper could also be incongruous, or incompatible with the effect you wanted. In that event, I suggest, maybe for next time, giving her a more expressive mouth. That could give the viewers' eyes direction and, depending on expression, draw in the viewer more and create a more interesting picture--making the viewer want to know why the tree-lady is smiling or whatnot. Which of course you don't answer. Because mysteries are exciting and memorable.
It's lovely in any event, but I wanted to leave a more in-depth comment if you are looking for critique.