Nicely done, the reflections are bright enough to hold their own and not look messy, the colors really pop, the background is simple but adds to the mood of the pic. I do think that if the shadows were softer I'd like that.
It's a very bright and colourful image that clearly meets the challenge so I can't see people voting it down for that. Exposure and focus seem fine, white balance seems spot on. The strong shadows might put some people off.
The composition feels a little 'tense', possibly because of the tilt on those towers. I find my eyes constantly moving around the outside of the image and struggling to find a single focal point. This makes me feel rather dispassionately about it. Personally I'd have given it a 5 or 6, so I can't understand the 3s you're getting. I'd have estimated this to finish around 5.5, but it may be scoring low because of the other 'cube' pics?