Agreeing with Darktwin here. Even if you going for that silhouettish look, you must always try to give depth to something, give it dimension. It will drag the viewer into the piece. When you're doing a textured background like that one, try to think in terms of fog or smoke. This mindset has always helped me get some 3d on the flat canvas.
Much the same crit for the last one - more importantly, think about your line. line isn't as unimportant as many artists would have you think. Contemplate EACH and EVERY line you draw, think about where you want it to start and where you want it to end, and how it will go from point A to point B. Later this will come a little more naturally.
I'm truly impressed with your progress man - very inspiring. Just keep practicing.