Let me preface by saying that I am no artist, and nor do I claim to be one, so I cannot claim to understand the intricacies of making art.
Now, moving on to the meat and potatoes of this critique, I think this is one of those oddly serene 40k fanarts. As a massive Eldar fan, it's nice to see artwork focused on them. But what I find especially interesting is that the artist chose to create a scene not commonly seen in 40k lore: an Eldar Maiden World.
In lore, the Maiden Worlds were planets the ancient Eldar Empire terraformed into paradises before the Fall, and they became hidden from the other races as the Eldar viewed them as the last hope for their species gaining a foothold in the Milky Way again. These planets are selfishly and viciously defended by the Eldar when they come under threat, and woe to any unfortunate sods who land on one.
As for the artwork itself, the artist has done a superb job with the lighting and giving a Maiden World the "handcrafted paradise" they're often described to be in lore. The landscape is a beautiful green with water being a clear blue, easily depicting the stunning beauty that the Eldar were known for immediately before the Fall. The colors of this piece really pop to the eyes, most notably the water and the jewels.
The statue of the Eldar goddess Lileath is also a nice touch, especially with the moss and growing on it - it says that this planet has been untouched by sentients for thousands upon thousands of years. And has probably been kept that way by the descendants of the Eldar who crafted it so very long ago.
A single Imperial ship floats silently in the atmosphere, giving a sense that this planet was just discovered by the Imperium. Even in their xenophobic and closed hearts, I am sure even Man can appreciate the beauty of this alien world - for it is not something they will ever see again.
I give this piece an 8.9/10 overall, as I wish the resolution was higher. Something like pretty should not be limited to a 720i.