It's kind of a cool idea, but there's a very steep learning curve. Figuring out how to set the joints so the fighter moves the way you want it to is quite difficult - in fact, some of the joints don't really seem correctly set up - as far as I could tell, they all had bi-directional movement, but there are many joints in the body (like the spine, shoulders, hips) that can move in more than just two directions. Maybe I was missing something, but I couldn't figure how to get any joint to move in ways other than the 2 given.

I think a tutorial would go a long way to make this game easier to play.

I'd definitely say it's not worth buying, certainly not for $20. Maybe if a tutorial was added, and some other things were added to spice it up a bit (like environments or at least backgrounds, music, maybe some skins for the bodies), it might be something to pay for eventually.