>G-goodness.. Thanks for the notes and feedback. I'm going to have to put that in a text file.
Yeah, sorry it's such a huge block. Sometimes I just want to explain something that's actually pretty simple and straightforward, but I have to explain something else first or it won't make sense, and that requires a much bigger explanation... and then I have to explain some bit of theory that goes behind that... and, well, ya know, it kinda snowballs.
Dang, you absorb stuff pretty quick. I can see interesting developments already. :3
One of the differences between the posterior regions of human and equine anatomy is that for humans, there's a cleft between the gluteal muscles (ie: the butt) and the back of the thigh. On a horse, the gluteals start on the top, and go down the side. (See: http://commons.wikimedia.org/wiki/File:Horsemuscles2.jpg Sorry, couldn't find one in English. See where it says "fléchisseur de la cuisse"? I'm not 100% sure of the translation, that's right about where the gluteals are. Sorta) So, that cleft between the butt and thigh? Horses just don't really have one of those.
Back to >>116068... the figure in the bottom right corner looks like it kinda sorta has a curve for the top of the heel, but it also kinda-sorta looks like the cleft between the butt and thigh of a human. Actually, it looks like both of those things at once, which looks weird since the figure's foot seems to be right up against their flank, and they don't actually have a calf. (All the ref pics I could find had highly visible unmentionables, which ponychan site rules prohibit posting or linking to)
This comes up in a number of your other drawings and sketches: >>113699 bottom right, >>114212 bottom right, >>113259 bottom right and middle, but I wasn't 100% sure if that was due to loose and fast drawing, unremoved construction lines, or if it was actually intended as part of the final drawing, or whatever else. Without knowing what case it was, I couldn't be sure how to approach commenting on it. Wasn't until >>114300 that I had a better idea of what was really going on, which is one reason why I had been asking to see more finished work. :3
I mentioned "complications" of mixing different anatomies and styles... this is pretty much that. Sometimes, things fit together well... looking at >>115987, the top left figure's shoulder looks very humanoid, but it works fine and looks great. Very expressive. Other times, they don't. In this case, the conflict comes out of two things: Humans have well defined gluteal muscles, while horses do not; and FiM style ponies have much higher heels than actual horses.
It looks like you're already working on some of this, particularly looking at >>116068, lower left, where the calf/thigh muscles are defined with a separate line than the top of the heel. I put together a quick redline, showing how the muscles on the back of the thigh look like where they meet the calf... rather than an arc, the creases form sort of an upsidedown Y. The upper green circle is the heel which is kinda lower down in the redline than in the original, because I wanted the muscle area to be clearer. (Also, this isn't really all that accurate. As stated before, most of the calf muscle are under the thigh muscle, so the visible part is mostly tendon. Like I said, this was very quick, I just wanted to show how the creases form.)
(Also, there's plenty of ref pics in Wikimedia Commons for the hindquarters of the horse, but most of them are NSFW, so I couldn't link to them on ponychan. Hopefully, the redline will at least give you an idea of what I'm talking about)
Anyway, hope this helps some. Developing a style takes time and effort, and sometimes weird stuff like this slips in unintentionally. Hopefully, these observations will give you a little more information to work with as you decide how to proceed.
Personally, I believe people are competent enough to solve their problems, as long as they're aware of the problem. In your case? Man, you don't waste any time working stuff out, do you? I'd say that's more than just "competent." :3
Aright, now I'm rambling. I really should be giving you more time to absorb all this information, sorry. Back to the sketchbook for me.