great!!
i really like it. I agree that the drawing isn't detailed but realistic as a more accurate word. I agree that some shading would definetly improve it a lot though it's a lot of work. But i also think that the fact that there isn't any shading and it still looks that realistic is really hard to acomplish and you totally nailed it. And definetly this needs more contrast, that can't be hard you open it in photoshop or whatever, put the max contrast possible and it will look much better with almost no work, i think you should do that and re-submmit it.
...oh and that guide-thing looks awesome