I really think that you're digging into those faces too much, especially the one of the dude with the beard. Try to pull it back some, and avoid over detailing. I think the next step is to start rendering out more of your drawings, you've shown that you can render just try doing it more...the lines make things flat. Anyway that's just what I've noticed, keep up the hard work!
come on push some more and get one of those portraits rendered up and finished, you will get such a lot out of it mate you will wonder why you don't do it before. It will be fun to do honestly mate come on you know you can, you cant just do still life for ever you will get mentally stale and jaded. Have fun with your art that's an ORDER soldier!!