Great background on this one, but of course the focal point is RAINBOW DASH. The pose may be overused but there's a really lifelike aspect to her facial expression. I think that might be because you colored part of her eyelids with blue borders rather than the black borders I usually see on ponies with their eyes in this "determined" expression.
I'm not sure what resolution these are originally done in, but it'd be awesome if your 16:10 version could be 1920x1200 instead of 1680x1050 (which 1920x1200 could easily be resized to by the downloader anyway, for those with low resolution monitors). Whenever I set one of your pieces as a desktop, I opt for the 1080 version, since the black bars seem the lesser evil between them or scaling up the smaller version.