First off, this could be entirely be my hand and the few hands I searched through on a gis, but they all seem to have a substantial extra bit of mussle on the lower part of the thumb. Also, the tendons should be a lot skinnier and more pronounced as you move from left to right, particularly the thumb where it connects to the knuckle. And the tendons should move more towards the center of the wrist, mostly talking about the pointer fingers tendons.
I can really only give these critiques as an observer and artist as I am still very new to blender. I’ve watched nearly if not all of the videos you put up on the site and I know I’ll be referring to them as I make my way through blender. Thank you for putting them up, they are very appreciated and the model is very good.