Nice, I like the choice of the shading and Luna's flowing hair style, very majestic. Plus her expression, lanky body structure, and coloring match up really nicely. Basically good appealing aesthetics overall.
She seems a little suspicious, but after a thousand years of moondust pies for dinner it'd be hard to open up to ponies again. (Pinkie Pie didn't help matters either.) I like how her face is in shadow but still clear enough to see her full expression (even a hint of sadness) while the her mane and left edge capture the moonlight for some neat contrasts.
Is her hoof raised as a signal to back off or as a perfunctory greeting (expecting a kiss or just a bump)? The crenellation of her horn is a visually interesting touch, as are the other places where you replaced smooth curves with corners and straight lines, most noticeably her livery collar, then on the edge of her shoe.
I can only hope that she's not actually on the verge of tears.