Well, as always,this picture has a lot of movement, emotion, and style expressed in just a single glance. The characters seem to be wordlessly telling a story, and their expressions add a lot to the overall effect and mood this picture gives off. The color scheme is well thought out and not blindingly sparkly or rainbow-y, and the fireworks are spaced just in the right way for it to not seem overcrowded, and dulled just enough for it to not take away from the interest in the foreground. The lines are consistent and have weight and depth, and the eyes-as always-are beautiful.
The only thing I can say for you to study up on or maybe fix would be the arms. Andrea's right arm seems to be a little blocky, and Spark's-especially on his right- seems to have no shoulder and appears to be chubby. There seems to be no hint or definition of a wrist as you travel up to the hand. Also where you hint-from the fluff on his arm-his elbow would be does not bend apparently from the picture.(sorry if I'm making NO sense....)
You might want to darken the shadows a little more and add colored highlights (from the fireworks) to the figures in the foreground, and maybe add a white highlight to the shinier surfaces in the picture (like the locket) as well.
This is actually one of my favorite pieces from you, though, so do not think to deeply on this. ^W^