I'm not going to go into great and vast detail but here's a brief critique;

The overall picture and composition is great. You seem to have a great eye for what makes a visually interesting piece which is impressive as people are usually taught this at college.

The only thing I think needs work (which seems the solution would be just lots of practice) is the torso of the girl. The chest is prefectly proportioned although it could be a little longer but the main problem is that the thorax (area below the chest) is too thin. While you have the shape right, it just needs a little more in the size department. You seem to have this problem quite often and I trust with enough practice, you'll get over that little hurdle.

Colouring doesn't need any comments. It's amazing as usual. You've a great nack for using gradients. The line work is very clean and the thick bold line that surrounds the parameter of the two subjects in the picture gives it the kick it needs. The background compliments them just right. Blue and yellow are a great combination and red adds to the list of primary colours which keeps it looking simple but not lacking.

Great job. Just keep working on your anatomy! Practice makes perfect.