Please take my critique with a grain of salt since I'm still a beginner. I really like your quick sketches that are 30 seconds or a minute as the majority of them are very loose and expressive. But it seems that quality is lost when it comes to your longer sketches as they look stiffer. If you're aiming for a more realistic look then try to lighten up the linework and rely more on shading to give the form to the hands/feet.
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