Its' amazing! I love it. And I don't think that the knife is bad at all. It juts at sharp angles, while the roof curves gently. it is really easy to tell the two apart if you actually are paying attention and see the knife (which i didn't the first time ^.^). All in all an excellent drawing!
Coloring, perspective, the use of shadows...very pro work definitely. I especially like that dark shadow that the buildings create, it makes the picture so much more powerful, and although I hate word dynamic, that is exactly what it makes this picture.
Heh. I cheated and used Sketchup as a basis for the perspective, with Chrissy's suggestion - it really is easier to build stuff in 3D and play with the camera than manually figure out where it should all be.
Google Sketchup. It's like extremely simple 3d modeling - you can do simple boxes, cylinders/spheres, that sort of thing, in a rendered perspective environment. I think it's actually intended for architectural work, but it works quite well for a general idea of how a given camera angle would look, which you can then redraw with details.