Your biggest issue with the animation is that the legs are twinned. What I mean by that is that they move together on the exact same frames in the exact same way. Try making one leg start the transition a few frames after the other and it'll look so much more believable.

Good work either way!

 http://cumhcroi.deviantart.com/art/How-to-Animate-the-dog-run-94970965

well actually i used this ^

about shading, i know i could do a better work but i had to animate it and it would be really hard to animate this dragon with detailed shading..

next time ill do better : )

 I love your rendering. I watched it for a while, and felt that there was something lacking in the animation, something emotionless. I realized that no four legged animal runs like that.

Refer to the following frame by frame of a horse running. I'd love to see this dragon with that life to it, really.

http://en.wikipedia.org/wiki/File:The_Horse_in_Motion.jpg

the animation is good but you should refine the lines, especially on the back and maybe add more shading to the body, it looks a bit flat at the moment.

 changed :) thanks for the comment

 Not bad but make the move faster changing its frame rate.