First off, I love the use of purples and browns to shade a what would be an almost entirely white animal and background. I think you did a wonderful job with the anatomy as well!
Vision: It is a great pose and composition. The cat is facing and walking to the viewer, and you captured the photograph's impact really well!
Originality: The moon is quite cliche, and I really think it would have been better to add a more realistic background, or at least something more surreal (such as a more pronounced waxing moon or sliver, possibly even stars), depending on what you were going for.
Technique: While the moon and "dream clouds" are well done, it lacks shading and values in certain areas. The moon is very light, and it just kind of blends into the clouds and what the tiger is stepping on. I think if you could have added more dark areas with a blue or purple it would really add to this. Also the sky is a dark blue, but I think is could have blended a bit better by having a more pronounced gradient of color.
The tiger also could use a little more shading in minute areas, but I know too much would take away from the "purity" of white. On the back and face, the black for the stripes seem to be a tad too dark, and it draws focus to it, but in an over-contrasted way. That is really the only place a black is used, so it seems overkill unless to add black to other areas of the drawing. Also, you used brown in only one part, and it just seems a little misplaced unless to add splashes of it elsewhere. Of course, that is just my opinion! (:
Impact: Overall, I really like it. With a few tweaks it would be even more stunning than it is now! ^^