There are some things which stand out for me in the picture, and I’ve probably already said some of these things to you, but they’re worth repeating.
Background – the fishbowl perspective of the horizon, and even the clouds, gives a good context but also puts the general focus on the main subject in the picture – the character.
The curved and slanted nature of the background and horizon gives the drawing a dynamic feeling of movement which is appropriate to this scene since Na’va is flying – it is as though the ‘camera’ of this picture is travelling quickly to keep in front of Na’va and can’t quite keep up with her and hold steady, or the camera is rolling around to follow her angling aerial manoeuvres. Also contributing to the dynamic feel is the showing of several different environments in the picture – underwater, above water, land and sky. I dunno how to describe the effect that it has on the picture, but I do like it. XD The choice of quite different shades of blue between the sea and the sky helps to distinguish them apart from each other easily at first glance (although the clouds have the same separating effect between sky and sea as well).
The Cumulus clouds – they have a realistic and painterly touch about them, with the various grey colour tones and warm sunlit areas on the clouds’ puffy heaps. I imagine it took some time to get them looking how they are. The ‘sea spray’ appearance above the water is nice effect.
The trees’ appearance is good too – they have that rough appearance/texture to suggest the presence of leaves, but the vegetation is indistinct and undefined enough to show that it is some distance away from the ‘camera’.
Na’va looks like she’s been drawn accurately and faithful to her ref – at least, as far as I can see. XD Her body has an interesting twisted pose and her two wings are at different angles to each other, which perhaps suggests she is changing direction slightly… it’s a cool perspective. The shading is nice and gives her depth, as does the blur effect on the tail (the part of her furtherest away from the viewer).
As for suggestions for improvement… I don’t really see anything that bothers me personally. It could be suggested to have the character appear either one-third or two-thirds of the way across the picture (either horizontally or vertically) so that it follows the photographic rule-of-thirds en.wikipedia.org/wiki/Rule_of_… but it’s not a rock-solid rule by any means, and it’s not something that I was concerned about, so I didn’t mention it in the stream.
To sum it up, I think it’s a pretty amazing picture! ^^ I feel like I've been rambling lol, but hopefully you got something useful out of that waffle of mine. <img src="e.deviantart.net/emoticons/x/x…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="93" title="XD"/> I like it, thanks for the commission <img src="e.deviantart.net/emoticons/s/s…" width="15" height="15" alt="" data-embed-type="emoticon" data-embed-id="391" title=" (Smile)"/>