Given the machine gun cutie mark, the character probably after my time... I stopped playing FF when it went over to the Playstation (except for FFTA, but I digress).
In terms of structure and proportions, the leg looks just fine. At this angle (if I'm reading it right, that is) the belly overlaps the leg, and the thigh overlaps the lower leg.
I'm guessing the character is supposed to have a slightly emaciated build... I dunno what the best way to pull this off would be, so I redlined as per a standard FiM style pony. I have to let you find some answers on your own, don't I? ;3 (IIRC, some emaciated ponies show up breifly in S2E17, Hearts and Hooves day, so there might be ref material there)
I did add a some thickness to the back of the back leg, and shortened it a smidge so it's level with the foreleg. Nitpicks, really.
For the forelegs, I tweaked the pose a little. In a neutral stance, the forward curve of a pony's leg goes as far back as it goes forward again, so the toe tip is in line with the top. Again, I added some thickness to the back of the leg. I also repositioned the far foreleg.
Of course, if s/he's not supposed to be in a neutral stance, this is entirely a toot point. Feel free to disregard.
Something else that may be a toot point, if you're not worried about show accuracy, are the proportions of the face I redlined. For the a FiM-style pony, the bottom of the eye is level with the nostril, at about the 1/4 mark for head. The point of the nose is slightly above this, overlapping the far eye. The distance from the near eye to the back of the head is equal to about the width of the bridge of the nose, which is about equal to the width of the far eye.
The bottom of the ear is level with the outside corner of the eye, for a typical rounded eye. For a Rarity/Twilight-style, almond shaped, eye the corner of the eye is a little higher up because the lid is level. The mane tends to come down from the ear and curve inward, rather than fall straight down.
Again, this may be a toot point if you're not concerned about show accuracy, or if I'm guessing wrong about the eye shape.
Aside from proportion nitpicks, the overall proportions are solid, and the character is expressive and lively. I find that latter point tends to get lost when an artist fusses too much about technical accuracy, or over refined lineart, so kudos on that point. The roots at the hairline totally breaks from FiM-style, but they look nice.
Yay, I talk too much.
Hope some of this helps... sorry if I went a little too deep into the fiddly little technical details, or if I misinterpreted what you intended to do (eg: the pose, or personal style vs. show accuracy).