First-off, I must use the disclaimer that I am by no means an expert in photomanipulation or even art in general for that matter but I will do my best to give a good critique from a beginner hobbyist's point of view.
Let me start by saying the things I like about this image. I really like the colour used, for one. It gives a really nice overall look to the image and makes it "pop" compared to some others I've seen. I also like the attention to detail. The feathers that were added floating around the wings add a really cool effect. The shadows are great too. I see that you made sure you knew where your light source for the image was and stuck to it. The shadow of the model works perfectly with the angle of the light hitting her. All-in-all this is a really nice looking image.
Now, I'm going to point out what I think could have been improved. The first thing I noticed when looking at this image is that the positioning of the wings doesn't make sense. The model is facing slightly to the side so the wings should have matched that angle. Instead, the way that they are in this image makes it look like they're coming out of her right shoulder or something rather than the center of her back. I realize of course, that it wouldn't be very easy to put the wings on an angle and have them look realistic too. I would have tried to use the perspective transform tool to try to get them at the correct angle. I also would have probably gone with a different colour for the wings like maybe black or white because I feel that the dark green blends too well with the background. This could have made your model visually pop out from the background more. The only other thing I can think of is that only one image was used for the background. While It's much easier to use a pre-made background, it's not always the best. It would have been a good idea to add more individuality to this image by say, using a different sky or adding some more subtle background elements.
In closing, this image is great. I really like it overall and I think you did a great job. Hopefully you can learn from this critique and it can help you in future projects. Like I said, I'm no expert so all of what I say is strictly opinion-based. Good luck with your future work!