I made an edit to Opacus'.

I like this. Being able to see the top of the grass isn't a bad thing, you just need to add depth and contrast so it doesn't look like a square.

I really like this. Though the eyes look really jagged to me, there are tons and tons of stray colors and pixels in unneeded places. It would be quite easy to just go in and edit it all out, it would look 10 times better. Maybe you're going to go in and polish it later, these are just nit picks.

Also the foreground raindrops look a lot like beams of light. I think maybe adding more or shortening them would help.
The leafs on the tree look like an Afro at the moment, some large branches going from the top of the skull into it would look better. (IMO)

Wow, I should really make an easy edit instead of trying to explain it like this.

More on that subject.
If you are trying to make a sphere take a look at this.

From what I'm Seeing right now, it seems like you're trying to make a saucer. There's two kinds of pillow shading, Bad, and Okay. Bad would be pillowing out from a center point like a lot of new pixel artists do. Okay would be what I've demonstrated, while it still is a form of pillow shading. (Just a cleaner more professional way.) Draco made a good edit on how you might go about making a sphere without using the dreaded pillow shading. Or of course you could incorporate dithering as well, but that's a whole other subject.

Thanks for all the great comments, but I need some critique. Especially on the head and feet.