Philomena is one of the most interesting things about the pony art community. So much different from what goes into the dragons and Spike, Philomena presents her own challenges. This artist rendition of her is striking, well-shaded, and mostly accurate, and I feel a bit silly offering any nitpicks. Still, that's what the artist wants, so suggestions I will provide.
First off, there are a few things about this image that are very noteworthy for how good they are. The shading in particular is very nice as in my ways it reflects the fact that Philomena is basically self-lighting. On any other character this pattern of lighting would seem random, but on Philomena it makes perfect sense. It follows outward contours of her body, since she's a living flame.
The proportions and shape are very nice. I like the attention paid to her keel. The keel is something that artists can get a bit uncomfortable with, since mammals don't have one. This artist didn't shy away from it, giving her that same strong profile she has in the show. The uneven countours of the tail feathers seem at first to be a flaw, but they actually reflect the fact that she's, you know, on fire.
The choice of colors and blending for this are great; they take firey look from the show and soften it into something slightly more realistic. At least, on Philomena they do. That missing half-star in impact come from how little she stands out against the background, which is virtually the same color.
Now, there are a few things about this image that don't work. The use of distinct lines on Philomena, while attractive and based on canon precedent, create a few problems. One of her legs (her left, viewer right) is almost perfectly straight, with only a slight contour at the ankle. The other (her right, viewer left) wobbles in and out for seemingly no reason. Having tried to paint straight lines, I know how hard it is. The only reason it stands out is because there are so many instances of dark lines being used to outline in this piece. You can be wobbly and indistinct for a dreamy or fiery feel, or you can have crisp lines whose contours are all purposeful and sharp, and not a failure of whatever you painted on to zoom in far enough. Your choice.
In general, though they are nice, I think the lines do the piece a disservice in some ways. It takes away from the realism and wow-factor in the use of color and lighting. Basically, the problem is not that the lineart is no good, but rather that the line art is good and the coloration is so much better it makes line art I'd kill for look bad in comparison. I repeat, the lines here are incredible, it's just that the shading and lighting is out of this world.
Then again, isn't trying to paint Philomena without lines the obvious thing to do, since she's on fire? The very risky, bold choice to include sharp lines with this kind of shading is why the standard Philomena pose is getting four stars in originality, not three. Any shortcomings this piece may have (or rather, shortcomings relative to its own greatness) are more than made up for by the risk inherent in choosing to use this style of lighting and shading with distinct lines in a final piece.
In short, this is an incredible image of Philomena. Its only technical shortcomings are like those of the people you read about in art history class: to dwell on them outside of requests for constructive criticism would be to miss the point of what they were meant to do. This is probably the most original piece of Philomena merely standing on a branch that you will ever see, and one of the most technically impressive, to boot.