I've heard a few different times now that horse walk cycles are just about the hardest thing to animate. Therefore, until you've had more practice, I'd suggest moving on from this project and trying out other cycles. Either a humanistic cycle, or possibly another animal. There seem to be a lot of key aspects of animation…
yeah you are right muybridge is a good source for reference...and about limitation, it was limited in a way like i cant move any Control only rotation was possible....
A good place to check reference for horse movement is in the Muybridge books. Highly recommended. Also, I can't say for sure, but it seems your rig limits you a bit.
To me it looks like in the middle of your horses stride he almost jumps and I think that is because the back legs are not coming forward fast enough or something around those lines
the problem is that the fore legs are moving simultanously (jump movement) while the back legs move crossed (walking). edit: mh, nah, looking at it again, both leg pairs seem to go from cross into simultanous movement :X bit of a weird movement mix.
quite allot wrong there, the head doesn't really come up in a gallop it actually moves forward and back more than up/down and the wrong legs are quite wrong. Take a look at some proper videos of the gallop [ame] http://www.youtube.com/watch?v=l48Kwa6izsE[/ame] for example.