This was fairly good of its kind. I think the only reason it has such a high rating is becase it persuades to our perverted side in some way. This is how most of us are, so you are appealing to a large fanbase. I actually liked how this wasn't as pornographic as some of the other stuff you have made. I think the best thing here is how well the curves are drawn. The curves on the butt are easily the best, but they all fit together quite well.
There probably could have been a background, but it's still very nice the way it is. I also like how the parts of the skirt are nicely spread out. It gives you the sense of a design similar to a windmill or something. A little gif is always good and yes, I am fairly certain they are allowed. It certainly wouldn't be enough for a full flash submission.