Still starving for contrast.

The hats shadow is almost invisible, why not use the darkest brown there?
And you need one more highlight color on the face: nose, glasses.

Boring??? Well, how about some background now, maybe with that bird in it?
Or some illustration of this:
http://www.google.com/hostednews/afp/article/ALeqM5hxS7rJjnpRg7yRU6vHm8b4KZHB8A

This has come some way, congrats!

I'm inexperienced at spriting, but I'd suggest to remove the outline first. At this small size, you need every pixel and color for shading and volume.

i made sure that the light was closer to the right than the left.

Far from enough! Just by 1px in fact, it's almost un-noticeable.
Also, the hat (mostly) and glasses (maybe) should cast a shadow.

Nice patterns, but there are strong readability issues.

Mirroring tiles destroys any hint at a light source you ever had, if any, so the patterns appear flat.
The only place with a little depth from light is the 2 rightmost dark tiles.
You will have to shade your tiles independently: choose a light source, decide whether the patterns stick out or recess, and stick to it.

I'd have some tiles with less detail too, and arrange them more randomly.

Having the same patterns on fore- and background is a good idea, but doesn't help readability, too. I'd reduce bg contrast.

Same thing with the sprite: he's got similar colors and values as the bg, so he blends into it. He's also 'pillowshaded', which makes him blend even more.
Again, think of a light source, and keep him contrasted, lots.

In this low-saturation setting, the green gun looks a bit weird.