It's a good start man, but I think it could do with some more work
Difficult to say that it doesn't look natural when I've never seen one move hehe, but I think this guy needs more weight. I think it's ok to have him move pretty fast - but the sense of weight is lost because you have the feet snapping down to meet the IK handle and the COG doesn't seem to shift the weight correctly (The very first step he takes looks almost right, he dips down and there's a nice shift... it looks like he's about to start a nice rhythm, but as the loop continues it seems to loose it) Also, on a weight issue, he seems a little too heavy at the front - the tail, I'm guessing would be used as a counter balance to the top half of the animal, but you have it just wagging around and out of sync with the rest of the body.
One more thing - The toes look great when the weight comes off the leg, but look strange when weight is applied as they're spreading after they hit the ground.
Hope this helps - and don't think I'm saying it's bad... I imagine it's pretty tough to animate a creature like thisand you have done a good job on the 'reverse' leg - just think it could do with some more
