I love sparkles. >///< You are right! Sparkles are awesome! <33

Design : Simple and generally easy to match with other items. Though I think you can play on the strap design. Currently, maybe due to different colours, some strap looked slim, some looked thick... kinda inconsistent, felt unpolished.
Shape : Form fitting is fairly easy to follow. You did the breast part well. The shape of the dress looked a bit odd on how it falls from below waist, at butt portion. The overall skirt shape seemed to be quite stiff. I can see that the dress seemed to want to flare outward from butt, but when fall to knee, it felt kinda harden, not flaring anymore. If you want it to be tight to body, then the shape should follow the silhouette of the avatar base closely.
Shade : What add to the contradiction of the fabric material being soft or harden, would be your folds. The way you shade your folds is quite straight, short. Which indicate stiffness. The hemline is so straight, more like pleated skirt type. If you want it to be flowy, remember flowy > windy, and how are wind portray in lines? wavy and curves.
Pleated folds are very strong lines, straight and bold.
Finally to the sparkles part! I think that is quite a success. Though you may want to consider different brightness of the sparkles. sparkles don't always shine the same white.

Have fun, good luck. <3
By the way, I would like a sapphire blue version and man! You don't have a black version? That is where the sparkles shine best. o>.<o