If you weren't limited to 640 pixels you'd have done much better. There's so much detail here, but at 640 it kind of looks like mush. According to your comments, you sharpened BEFORE resizing? That could be part of the problem. Always do your substantial sharpening at the last phase, and definitely after the resize.
Beautifully structured image. Nice composition, excellent exposure and really fine processing. The result is, to my admittedly non-expert eye, perfect tonal control. 9.