Robotic mega-penis.

Mmm, so so, I don't like the shadows and the composition.

thank you, for coments

The shadow on the side is not needed, the sun does not reach that place anyway. That is the only 'mistake'.

Furthermore it is just a bit of boring, big, not detailed..

Some surfaces in your pic that facing light are bright, some are dark. You gotta sort it out.  Also look how you placed your decorative line - in one place it bends with the surface, in other it goes through it. And color of this line is not the best choice - it is barely visible on top, use more contrast. Also rendring is rather empty - mainly one color everyhere, one material, so it is not very interesting to look at.

I'd suggest using more tones of grey for different sides so it would look more realisstic. Also for first try is better to work with much smaller pic - so you'll see the whole pic, will spot mistakes by just one look and, of couse, rendering will take less time.

By the way, look under magnifyer how lovepixel does it and nick some ideas (like his way of drawing edges, little features, maybe even palettes - it's all working for making pic better!):

http://www.lovepixel.idv.tw/page/main.htm