I'm going to drop a bomb on you, hold on to your hat.
The main problem in all the paintings is the flatness of them. The forms aren't rendered correctly. The colors are very narrow in saturation, light/dark, everything. This you can better by doing things like still lifes and such. I have the perfect thread you could read for this: http://www.conceptart.org/forums/showthr ead.php?t=107217
You can brows around on that forum, they have great stuff on there.
You also need to improve your anatomy greatly. I don't know if you have studied anatomy at all so far. But this is very important! I suggest you download a PDF of "Figure drawing by Andrew Loomis" and draw everything, read everything, learn everything. But remember: you can keep studying anatomy until you die before you master it, so don't worry if you don't get it right away. I've studied anatomy for years and I still haven't got everything, faaar from it. But make it a habit of studying these things.
Set up a schedule that you follow every day.
Eg. Monday - still life and anatomy from loomis Tuesday - Portraits from photos and drawing muscles from bodybuilders.
Fill that schedule with important things, and follow it everyday . or as often as possible and make no excuses.
Art is difficult and weird as it is, people think that you can just keep on drawing the same things and eventually you'll get it. It doesn't work like that. There's technical things behind art as well. You need to know the rules before you can break them. So things like style comes eventually, don't care about that stuff at all in the beginning.
Hope this helps. Take care!