Yeah, the body is kinda skinny.
Trivia: these guys were featured prominently in the G1 cartoon, and were called seaponies... not merponies. But then, seaponies looked more like seahorses: they had fins instead of forelegs, and no fins on the tail... it ended in a little curling tendril. Also, they sang. A lot. Which is where the line "shoo-be-doo, shoo-shoo be-doo" comes from. That's right, it's buckin' canon.
But, basically, this design is distinct enough from the classic seapony that it could merit a it's own name, if you wanted. In classic greek mythology, a half-fish-half-horse was a hippocampus ("hippo" is greek for horse... hippogryph, hippalectyron, and, yes, hippopotamus). They had brass hooves, how pimp is that?
...I digress. Merpony works just fine, since this is not exactly a seapony, and hippocampus is kinda obscure and sounds silly anyway.
The tail fin splits. Fish's bodies usually come to a rounded end at the back, and have one large tail fin that radiates out from it. The fin might have a V shape to it, but it's still one fin (eg.: this guy: http://commons.wikimedia.org/wiki/File:Herringadultkils.jpg).
The fore legs seem rather long. The height of a pony at the shoulder is about the same as the length of their body. Aqua's leg is about as long as her body, and that's while it's somewhat tucked in, and from the elbow down alone.
The upper forelegs are rather thick. Most of the tapering in a ponies foreleg happens at the lower half.
Well, uh... it's really small. Points for that, I guess. not much else to say, really.
>Thank you a lot for the critique!
You're quite welcome! It's my thing, actually: I'm kinda the resident critique guy. :3
Back on topic...
>Is it better now?
Better indeed. The hatching directly next to the hooves is still slightly lighter in shade, so there's a little bit of halo, but it's much less conspicuous.
I could nitpick over the hair: The edge across the forehead doesn't come as low as it does in the show, and it connects to the edge of the hair on the side. However, it definitely has more of the elegant silky look of Fleur's hair, rather than the sport spiky forelock of Dash's, so Mission Accomplished. If you're that worried about show accuracy, it might be worth tweaking, but I don't really see a need to.
I do notice the changes to the hair coming from behind her ear... much less confusion about the back of the neck, but not as show-accurate: it looks much thicker, and doesn't have the "notch."
And, now that I'm looking at it, I just noticed... In the show, the mane coming down her neck has three locks: one that ends in a point, and two that curl forward; the hair behind her face, the side that meets the hair coming across the forehead, has a lock that comes to a point, and one that curls backward.
In >>116250, the mane coming down the back of her neck has one backward facing curl and a point, matching the "forward facing" part of hair, rather than the part that comes down the neck. Again, kind of a nitpick... the first two times I took a good, close look at the original and double checked the image refs, I didn't notice it .
It doesn't matter which way the head is facing, either: the edge along her forehead always follows the direction she's facing.
Ah, the joys of quantum mechanics: "the act of observing changes the observed," so pony's hairstyles can flip depending on what what direction you look at it from. It's science, so it must be perfectly logical. Eee-yup.