I got some suggestions:

- doesn't the thumb looks a bit flat?

-maybe u can make that bone in the wrist to bulge, I dont know its name in english, but if your right hand is facing downwards you can see it in the right flank, if you know what I mean.

- you can make a crease all around the nail, i mean in the place where it is atached to the flesh, or if you dont want to, maybe you can paint it in a separater layer of texture, as the one you are using now is a procedural texture, isn't it?