I'm not an artist, so I apologize if my opinion is poorly worded.
Despite the expression (one I usually wear, as well), this seems a little friendlier and softer (more rounded) than many of your other recent illustrations. I would say that you should have spent a few extra minutes smoothing out the lines, especially around the cheeks, but if you're experimenting, then that's best left for later works (if you decide to continue on with this style, that is).
It's simple. I like simple. I would like to see her though as a full-body image, rather than as a bust, to get a better idea of what sort of "look" you're aiming for with your characters. Right now, I'm only guessing.