First off, I must say that when I first saw this in my deviation box, I was quite impressed ... this is a very big breakthrough for you in my opinion! As you know, this is my first official critique, but I'll attempt to make it good by explaining why I rated the way I did and suggest some things you'll find helpful (I hope so, at least! )

According to dA, when rating for vision you should ask yourself, "does the artwork present or reflect a point of view, theme or idea?" I see that as an opinion, a firmness of thought that the artist represents in their work. The idea is quite clear--you clarified it even more in the artist's comment--but it's hard for me to tell exactly what stance you take on Zim and Dib as characters in this one piece. Being your friend, I certainly do know what you think of them because of conversations and your other cool stuff , but to an outsider looking at just this piece, it may seem confusing. It certainly doesn't strike me as romantic ... perhaps the other, more canon, more violent side of their working relationship.

Originality is a pretty clear-cut topic. I've seen art of Zim torturing/experimenting on/fighting with Dib on many occasions, but you take it a step further than just that. I haven't seen a deviation set in a snowstorm like this one is! So I give you one half-star above the norm for that.

Now for technique, which is also self-explanatory. The composition is very pleasing to the eye: nothing is in the exact center, the main focus put on the sides of the piece. I really enjoy the more painterly style you went for in this ... of course, typical computer-generated smooth gradients have never appealed to me much The subjects fit in well with the background in terms of their highlighting and shading, and I can tell that there is snow blowing between the viewer and the subjects ... it's a nice touch! The perspective and the way Zim is not fully visible is neat too. One thing that I would love to see more of in your work is color. Yes, I know the characters are in a snowstorm, but I think it would have been neat if there was some other color value in the background rather than just gray tones. A little light blue would have added more overall interest. You also shouldn't be afraid to throw different colors into the shading on the subjects ... it can turn shading from a boring necessity to a masterful detail! A little variation in the shading for different materials would have also been cool ... I can tell that you gave the metal some thought, so you really just need to exaggerate things a bit more in your shading to make it more interesting to look at. Brighten highlights on metal, saturate shading on skin, sharpen shading a bit on shiny material (like Zim's gloves).

I rated you highest on impact for a reason. dA states that impact is supposed to strike a chord with the viewer, blow their mind, make them think, and I did think hard when I looked at this and read the artist's comment. What is the world like when you don't know what's real and what's an illusion? I was reminded of mirages in the desert, when you become so thirsty and desperate that you see the thing you want the most far off in the distance: water. So does Zim really want to see Dib at that moment? To fight what I'm sure must be cold loneliness in the midst of a snowstorm? To see something that defines and reassures him--his biggest enemy? Or is that simply a figment of my imagination? Definitely some food for thought!

Anyhow, I hope that this critique explains my thoughts fully and helps you ... I tried to make it as constructive as I could! Overall, this is a really cool piece in many respects and you should keep it up.

Once again, an awesome work. Both Zim and Dib look amazingly amazing, and the detail and attention you pai to each fighure is amazing. There is excellent prescence and perspective going on in this pic, and the detail and color you used when coloring Zim is amazing. I especially like his gun. You get extra points for the gun XD It looks like Zim's totally gonna blow Dib away. The only thing I see weird about this pic is the snow. It doesn't particularly look like snow, but more like a really thick mist. If you added a few lumps of snow on the ground, or snowflakes in the air, or even some snow on either Zim or Dib it would look a thousand times more like what you were going for. It may not be a snowstorm, but the effect of limited visibility and the misty quality of Dib still make it an extremely effective pic. And one last thing; zim's highlights and shading made him stand out from the background and the storm that much more.
This wallpaper is made out of win.