i quote skeddles,i don't like much the dithering but the rest is very nice :3
The dithering kind of takes away from the piece imo, but the colors are really great.
This look good for me, but i'm still only a beginner. Hair look sexy, and also clouds are great!
One thing more : your isle stands too much out of the sea, could add transparent waves that would die out on the sand, for a smoother transition, see ?
Keep pixelling, your girls are really refreshing 
EDIT: I don't like much your blue shades (especially in the sky). Are you brave enough to try new colors ?
love he foot and grass, perspective seems off though (I'd probably move the oceanic horizon line up a bit).
It's a great concept, and could make for an amazing image, but as ekobor said, it looks weird at the moment.
I think you chose a difficult pose and angle, and got stuck in some problems.
Mostly: there seems to be a face in her head, looking up to the left. Even zooming, I can't decide what it is: a hand in her hair? If so, it should be more obvious, maybe show some arm and elbow too.
The right foot is weird too. Both feet are too big, and although their curve is sexy, it's not natural: you wouldn't sit like this for long.
The left buttock and thigh could use better lighting, so far the foreshortening doesn't work so well.
These problems are worth fixing! Maybe get help on the forums about anatomy, I'm very limited in this respect...
Some small things: the lines near the horizon (waves I guess) don't work because of perspective, I don't think they're needed at all. The sky is nice, but I think the dithering is too regular; maybe try a more random and/or horizontal pattern?
Don't give it up! ;-)
(Edit: your answer came before my post)
Is this supposed to be viewed at 2x?
Because at 1x she seems filled with anatomy errors, but at 2x they seem to be fixed. :s
Otherwise, top-notch~
The pose seems a bit weird. Aside from the left foot, it's hard to tell which way she's even facing. Does she have her head turned all the way 90 degrees?....Actually it looks like more than 90 degrees. The right foot and hand showing are too confusing.
I agree also about the dithering too. The clouds look nice with it, but too much for the sky.