Lineart and shading is really nice, however your colors are pretty saturated. You've got a good amount of contrast right now, but it wouldn't hurt once you've got those saturation issues worked out, to do a little bit more with it. I like the piece though. The animation is pretty... well, it's just not smooth. Walk frames are pretty hard to do in just 4 frames. Expand that to something like 6-8 frames though, to fill in the gaps, give him a bit more motion, animate other smaller details, and you'd have a pretty nice piece. Good job.