you've got most of the feature right here, but I would imagine there's something about it that feels off to you. There's a few little things that contribute to this feeling, most of them have to do with the way coloring works. For example, the dark sweater she's wearing lacks shadows and multiple shades. Ask yourself, what is the material? How does this material reflect light from the given angle (light from above, camera near perpendicular to the light source)? How does it create shadow? The torso space immediately under her right elbow would have shadows, right? So how would you contrast the shift in light? If it were me, I would lighten the overall color of the sweater by 10% or so and then create the shadows. I can see you have a general texture and outlines going, but they're all dark on dark making them exceeding difficult to see. Next, I know the background is take from a game, but what can you do to further blend her to the scene? You can see in the background the colors are soft and blend gently. The artist of that background didn't use strong outlines to make the pillars visible, he/she used contrasts in colors to make it stand out. You might want to check her right thumb, the thumb manipulating the MP3 player, it looks to have an extra joint. Also compare it's size to the size of the knuckles, the size ration isn't the same across genders and that ratio looks like a man's. You might pull the sleeve back some and show the wrist too (master drawing them in the process). A nice way to make the headphone chord stand out from the outfit is to give the outfit a filter effect, change it's colors and leave the headphone wire alone. Another option is to erase the wire, add an antennae to the headset. I'm out of time right now or I'd continue, if you want more from me, just let me know via reply or note and I'll post a continuation. If not, then I'll assume no.
I like the picture a whole lot, and I find it a refreshing quality that I haven't seen in a while. I feel you could have used the empty space a bit better, maybe included some action in the background. People walking about, waiting, etc. Unfortunately, the realm of Vocaloid has featured SO much it's hard to be original. The only reason I marked originality down was because of the fact I've seen a few pictures like this. But even amidst the flood, it feels like this piece has it's own feel and still that stands out. A great piece of work that caught my eye. Good job!