Hey, awesome piece! I really love Sombra, she is an awesome character 
There are a few thins that look weird with your piece, anatomy is not quite right and the colors are far too saturated everywhere, making for a very distracting painting. The background is incohesive and doesn't contrast or benefit the focal point very much, the work is also half cel-shaded and really lacks the depth that lighting (and in contrast, shadows) would give. Shapes are therefore a bit messy, and makes this feel quite flat.
As for the anatomy I was talking about earlier, her head is too small and her thighs are almost explosively too big. I'm almost certain that her weapon is bigger than that too, and that glowing ball on her hand makes little sense considering the character, you could've added some sort of representation of hacking, which is her primary skill. And this is made easier by her gloves that are technological and make the hacking itself visual, as seen in her cinematic.
And back to colors, there is a lot going on here and you usually want to be reserve with colors so to guide the viewer just like with composition (this is why lighting is also important). Looking at your shadows again, I just have to say that it is important to create clarity when making forms, for although we have to be subtle when creating good art, when being shy with light and shadow, all you are doing is blurring out the shapes.
Anyway, I really like this. Hope I didn't sound too negative, as I'm just trying to help! And I hope it was helpful, haha.
