Yep... I've had my fill of horses! They are difficult to get right as they are so familiar to everyone.
I'd like to see a proper playblast of this - looks like you use a screen capture prog so it's a little bit laggy.
There does seem to be some issues with the deformation - that's a rigging thing, and four legs is not easy!

Just be sure to get some movement around the shoulders... In fact the front legs stretch out quite a lot on a gallop.
One thing that did strike me about this anim is that the head seems to be in reverse... I mean that it pulls back when it should push forward. Have a look at some reference from Muybridge. (fantastic reference material!)
Just found some great reference here on wikipedia (has a Muybridge gif)
http://en.wikipedia.org/wiki/Horse#Gaits
Or another one here is quite cool
http://ultimatehorsesite.com/info/gaits.html