You have a good composition, strong use of cool and warm colors (I like the use of cool colors, makes it more jungle-y) and you've got just about everything blocked out. Make sure you pull out your references when you start going into detail.

Can you keep links to the progress of these? It will be nice to see how everything is coming together.

I'll comment more as you make more.

A few things about your characters turn me off.
They all have the same body shape. The eyes are weird too, the characters seem to be looking down and back. EYES FORWARD!
The head isn't nearly as round as you depict it. Practice basic human anatomy. It'll help a lot in the short run and even more in the long run.



I don't like black outlines. Just my personal preference. Why use pure black when you can soften things with a smoother transfer or contrasting color?
Try not to get caught up on details. These guys are going to be moving around on a screen, people won't notice most of these details. Get the general look blocked in then slowly work smaller and smaller. That's sort of the painterly approach, but it does work. For me.

Try mixing a little bit of color into your whites, blacks and greys. It's fun and will make them a little bit easier to look at.

Really appreciate the C+C, thank you all very much.

Took into consideration what Rydin said. It's not really executed well but the idea is there. It'll improve as I keep picking at it and playing with references.

Yellowed the leaves a little, they could probably use it a bit more. Ripped off a bunch of leaves.

EYECRAFT! Means a lot knowing someone saw a level of urgency in the tree's actions. Wish I read your comment earlier, the dead tree idea sounds good. Definitely worth trying. Rocks were erased, dunes might move in soon. I'll try to sprinkle in signs of former life. It'll make his search for water that much more against the odds. Right?



Thank you for the C+C, hope I'm headed in the right direction.


EPDITE!

Small changes with the colors and playing with layering things in the background.
Are the dunes too patterny? Clouds are too sparse I think but I like them more than the previous ones.
I'll probably play with the leaves later tonight.
I'm thinking of adding a bright red bird on his outstretched arm. Might scribble that into existence soon.

Thanks to everyone who has helped me so far.

This is a really good start for your first pixel art.
I don't mind having an extra color in that sprite, I think it does have a NES feel to it. With 2 more colors it could probably still have a NES feel. Though right now it looks like you're using 4 colors because the skin and the white are so close. If you're not using the NES palette I suggest darkening and saturating that skin tone.

Arne had a really in-depth thread going on not long ago about a pseudo-NES project. He didn't have the NES palette but he stuck pretty close to the same restrictions. Since you're using XNA (I assume this is intended for computer or XBLA) the game doesn't need the exact restrictions. You might want to consider using those restrictions as a rule of thumb.

Arne's thread.

The technique Helm is using will really help you define forms.
The wings/hands don't make any sense to me. Doesn't make any sense in the sketch either. Might be a bad design or my lack of sleep.