Erm, how about getting the actual image of your first piece of artwork rather than a thumbnail? Due to it being cropped; then perhaps we can evaluate it properly.
And as for your second piece, can't really say it looks quite like pixel art. I'd say what you need to work on would be the shading and the outline. On the outline, you have many excess pixels (which I'd recommend erasing) also, don't only use black for the outline; try using different shades of the main colour you've used. For instance, your main colour scheme is green, therefore use different shades of green for the outline. Depending on where the light source hits, you'd have to use different shades for a certain area on the outline; darker shades for areas that would be expected to be coated in some darkness and a much lighter shade for where the light source is actually facing, it would make your piece look much more 3D and pixel like.
Now, the shading. Refer to
this stickied thread for other shading forms you can use. I'd recommend trying them out, for it may improve on your method of shading, which right now doesn't really improve it's presentation.
Otherwise, nice try, keep at it.
EDIT -- The same goes for your humpty-dumpty piece. It's nice but it requires most of the content I've stated above.