Love it! Wonderful atmosphere. Somewhat nostalgic for me, since it hasn't snowed much at all here in the past few years. You can practically hear the soft muted tone that snow gives everything
I agree with others, the blurred snowflakes are a very nice effect. And Luna is GORGEOUS! And the lighting and shadows are all very well done.
If you're looking to improve your background drawing, then go back over it with a smaller brush and refine out all those visible brush strokes, and generally sharpen and add more detail to everything. You can keep on going smaller and smaller until you're in pixel art world if you want. But you already have the base done here, which conveys the vast majority of the emotion of the scene, and that's what counts. Any more detail added is just icing on the cake And actually, I think this picture would be pretty easy to over-detail to the point it becomes distracting from the overall feeling of it... and distracting from the lovely Luna. So I'd definitely call it a mission success.
It's difficult to say something about this background style... But I'll try it anyway. ^^
The picture with it's background looks pretty harmonic. The blur effect in foreground, the snowflakes and the moon look good, too.
Everything else probably needs a bit of experimenting... I only can tell you some things you could try, since I have no idea how it'd look like. The elements more in the front should maybe be more detailed (perhaps using a finer brush setting?), the further away they are the less the details are of interest anyway. I hope that'll help you a bit for your next background practise. :3
What a lovely mood and great scene all around. The lighting is gorgeous as Princess Luna strolls through the forest as a gently breeze throws around some loose snowflakes. She looks so pretty to begin with, but even more so as she stops in mid-step so delicately as she looks up. Perhaps even she's in awe of how awesome the moonlit snow makes the forests beyond Canterlot look under her full moon.
Then again, among the title, her desire to soften her tone, and the fact that she didn't get any singing parts in the wedding episode I can almost imagine that she's singing softly. Perhaps she's a little self conscious about her singing voice as she sings a lullaby to all the trees and plants and hibernating critters.
No matter what it's a great view of her softer side along with being a beautiful picture of her in general, plus a gorgeous and wondrous background too.