I think one of the problem ares on this are the eyes and cheeks,
I think you should look at some reference of some orcs and really study whats going on in those areas, I think the mouth also needs a tickle here and there.
Get a mirror and look at your own features, pull some faces and see what areas do what and you'll get a better idea of your facial anatomy, which is important whether its an orc or a human head, especially the eyes/eyebrows where theres lots of compression of muscles going on there. Also look at the difference between a man and a womans brow ridge, a mans is a lot lower than a womans, also the woman eye area is a lot smoother too.
I know its a first head model and I can appreciate how hard you are trying as it can get extremely frustrating at times. Also concentrate on the face itself at this stage and make it as best you can and then worry about the helmet, teeth and other details later. Oh yeah, get plenty of reference too, you can never get enough of that!!