RAWR! Phew, just took a look through your whole sketchbook, and the progress you've made is very impressive. I'll agree with what the other people keep saying - in your early works the nervous lines were very obvious, but you seem to have dealt with that really well. Your facial studies are excellent, it looks like you've put in a lot of work there. Your colour works are pretty impressive too - looks like you have a pretty good grasp of colour and value, from what I can see.
Don't forget about the rest of the body though - your studies on those from the Bridgeman book look good, though nowhere near as developed as your facial studies. Don't forget to apply the things you learn in anatomy books to your own poses, instead of just taking it in in the position they're drawn by the author.
So yeah, keep at it! I'll try give a more indepth critique at your next update, instead of trying to do a general one like this.