I think it would be a good idea to learn drawing realistic before creating your own cartoonish style. At least that's what most great animation studios do. It took moths to settle on the style they wanted to draw 'Ed, Edd 'n' Eddy' in, for example :3 At least try to look at references, even when drawing cartoonish. Find 10 photos. Find 100 photos. Look at other artists and how they draw. Stuff like that ^-^
But right off the bat, I noticed that the hooves didn't stand on flat ground. When drawing, it helps a lot to try and remember that the creature doesn't just float in the air, but actually stands on something.
Next I fixed the hock. I'll give you credit for that; it took quite a while for me to notice in which way animal legs bend, so you're already quite observant! ^-^ unless you were going for a 'stomper-style', where the foot is unrealistically big (in which case I apologize for fixing that), the lower leg is always thinner than the upper leg.
I added a sway to the back. Again, looking at real horses, unless they're unhealthy, their back will always have a slight sway.
Cartoonish horses don't necessarily have as straight a nose as real horses, I just like it that way ^-^'
I made the ears pointier
Added some hooves. Again, not necessary when drawing stylized, just a personal preference ^-^'
And lastly, I made the bum bigger. It makes it a bit more harmonic when the backside appears heavier :3
Drew some more realistic stuff just for kicks