First, her face is great, and I really like the colors for the skin! There a couple things I noticed:
The proportions are a bit off on his size compared to her, he is much bigger than she is(this might be a creative choice, but his body is a bit odd looking...)
You also need a bit more light on her hair, make sure to show the "clumps/groups" of hair and not just small strands.
There is a lot of canvas space that is empty, so a blurred background that is less saturated would really bring it together. A place, such as a battlfield, room, forest, ect...
Fix those things and a bit of polish and this will be amazing!
Good luck! let me know if you have any questions and I can do an overpaint to illustrate what I mean.