This is my first critique, and well, I've gotta say, this is amazing! I love the way the piece portrays Luna.
Me, being an eye person, absolutely fell in love with the eyes! Hell, I love the way you do eyes. They're not hyper-realistic, but their not overly cartoon-like, they are the perfect mixture.
And I love the shading, getting those deep, rich, blue tones really brings out the piece.
And lastly, the mane! I love the way you styled Luna's mane, it fits ehr perfectly! I fell in love with it at the first glance!
Overall? 10/10, hell, if I could, it would be 100/10.
Very well done, very very well done.