K, here's what I notice. Oversharp on most. And the renders are skewed and stretched oddly. Work on that. Lock the aspect ratio when you resize. That will help you a lot. Also, do lot's of tuts. ^_^ They will help you much. Keep workin' at it bro!
They are really messy and low quality, some of your renders are stretched and skewed, you should try some cleaner looking designs. Use some clean smudging, maybe some C4D renders for effects. Depth is a big part of sig and LP design. You need to have your focus point stick out, so its the main thing the viewer notices. Color is also a big part, you need more visual interest, through color, detail, effects, and lighting.
