Contour line proficiency: acceptable. Next step: Depth. yo.
Very nice
My fave is the shoe, it has the most umm... 'pop' to it, y'know?
Pic by pic commentary:
calculator: I think maybe you've placed too much emphasis on drawing out the characters/symbols on the keys and not enough on the actual shape and feel of the calculator. The bottom half where the cover is behind the main part is nice, but the keys have very little depth and the side of the calc. is not any darker (or lighter) than the top. On the left side, put a little bit of shadow under the fingers perhaps, to intensify the illusion that they are above or touching it.
eye: This one is nice, except you've got a very very dark pupil, and the rest is really light. You need to echo that value somewhere, perhaps in eyelashes? This would also make the piece feel a bit less naked... it's needs eyebrows or something (probably neatly plucked and trimmed to appease SARN)
hand(s): uh, nice. That's pretty much it
leaf: once again, nice
crumpled paper: This one, like the eye, just needs more contrast, more dark darks inside the folds and in the interior areas. It'll make it stand out a lot more,(unnecessary comma) while adding realism.
shoe: This one has nice contrast between lights and darks... the outside is all white, the inside is shaded. It gives a lot more dimension to it, as does the blocky shape of the little treads >_< on the bottom and the way you carried the line from the midpoint on the tongue down across the upper part of the shoe a bit.
skull: lower jaw is too big? the eyes should be a tad darker, unless your reference pick was taken with a flash camera or somefink.
That's probably an annoyingly large amount of suggestions you didn't want, but, sorry
I wuv youse.