It is hard to critique such a strong portfolio...you really are doing some amazing stuff here, especially in the latest ones with the bits of photography you are using.
I find at the moment you have really got the rendering, colours, and textures down. I think that therefore you should focus on other aspects besides the technical finishes.
A bit more attention to keeping the viewer's attention on the focal point could be made. I think this can be achieved by subordinating some elements of the picture a bit more. For example, in the first picture my eye keeps getting led down to the bottom left corner (which I assume you do not want). That area just has so much more texture and is a little bit too contrasting in terms of colour are value. Another example would be the ninth picture down with the man about to punch the other one. On the right hand side of the image, the light upon the man's forehead is standing out a lot to me and is a bit distracting.
Your light sources are a bit inconsistent in a couple. The man with the robotic arm in the fourth image has a warm strong light on him from the upper right. This light isn't appearing on anything else in the picture though, the ground is painted as though there is a completely different lighting situation. In the same image, there appears to be a fire off image at the bottom, and it can be seen reflecting on the gun he is carrying, but why is it not also showing on his pants/shoes? In other pictures you have put in a bit of a rim light (the elephant man and snowmancer), but this light has no source and is only appearing in a very small area--if there was an actual light source causing it, the rim light would affect a few more areas, even if it were very subtle.
The last thing I would like to mention is the weight of things can be taken into account a little more. On the man with the robotic arm, he is carrying what appears to be a several hundred pound gun. Yet his pose looks as though it weighs nothing at all. Certainly he would feel its weight and his pose would change accordingly. And in the snowmancer image his weight is all leaning to the right. He would be off balance with the positioning of his legs, and his staff is not positioned to help support him. I would reposition the foot near the staff to the right more so as to balance him out (the legs also may be a bit short at the moment).
Anyhow, very solid stuff here...it was hard to critique and I was being really nitpicky. But I think just paying attention to the small things is what you need to do because you have such a solid understanding of the major components of art.
"Complacency is the womb of mediocrity. " -- Jason Manley
"If you always put limits on everything you do, physical or anything else, it will spread into your work and into your life. There are no limits. There are only plateaus, and you must not stay there, you must go beyond them." -- Bruce Lee
Hi, I like it a lot. Only thing that I can notice, but wich im not sure is it good or bad, is that images are pretty low saturated and blended. so I feel that instead the characters or other storytelling ellements, the atmosphere becomes the subject of the image.