My first impression was that of a grown-up Scootalo, visiting the treehouse after some years. But that impression changed and shifted quite often, while I was looking at the picture.
Sure, the technique is good, the lighting, colours (especially the colours), etc. but that only would make the picture good. What makes this picture great is the clever use of hints while keeping back some details that might help to construe the story told.
For example. Two capes are already hanged up, Scootalo brings the third. We do not know if Sweetie Belle or Applebloom brought their own or if Scootalo gathered them. Her expression seems melancholic, but we do not see the real cause for that. Is it because she realizes the decay a and deep feeling wells up, that is perfectly normal if you are somewhere, where you have not been for a while and see how time caused the dereliction.
Sure, we see the abandoned treehouse, but nothing more. Scootaloos Cutie Mark (if there is one) is cleverly hitten, adding to the aspect regarding the capes.
In short. It leaves very much room for interpretation and I had a lot of fun constructing quite a few scenarios and little stories in my head.
Regarding the more technical aspects:
The lighting is good and draws the eye to scootalo. It took me some time to notice the capes. the greenish atmosphere just adds to the impression of a mysterious and rather deep forest.
The fur and mane in their brighter and stronger tones help to draw the attention to the motive itself.
There are some vey nice little details, that help to spice the picture up without causing a negative effect to the mysterious, calm and melancolic feel the picture generates.
The only only ONLY thing that throws me off is the little shadow around her eye. The ONLY thing. Awesome awesome work. It's a lot easier to critique than actually make the effects and draw it right myself. Trying to work on that.