number blocks are too small for such a big picture, it makes the counting of spaces difficult and you are more likely to lose count. It's also annoying because the cluster that form could be anything along the line since most numbers are small enough to fit.
This was so difficult to get started. Once it finally caught, it flowed pretty nicely, but still took time. I think I actually worked on this one pretty consistently, and it took almost 3 hours. Cool concept for an image, and it works well.