I'd warn against a lot of shallow detail. Most of these look like you just sculpted your volumes then ran a stamp over them for detail. It makes them look very flat. The skeleton and the arm look like good studies to me, however with the head it looks like you went for detail too soon. He looks like he's puffing up his…
Did you mean not to link your actual portfolio? http://sandro3d.com/ It looks good to me. I'd like to see a final game character that isn't a freak-out monster. Just to help your marketability.