Too many folds on the palm.
It looks like hes wearing a gloves.

Shape is really nice but try to give more pillow look to the thumb,add more tissue, you still got some too deep folds at the roots of the fingers.
Outstrech your palm and you will see that folds are very shallow, in that pose bump map can do the job, but when you close your fist then skin doesnt fall in but muscules tries to overlap and so deforms the skin.

Model the volume of a muscules on the fingers not folds between them!