I like him! I agree that something about the arms is off. I think it's most apparent in the diagonal up sprites. Both of the arms in those 2 sprites are the brightest skin tone. Maybe add more shading to them.

Where is the light source? If the light source is in front of the character, then the leading leg during the walk should be the darker colour, and the trailing leg should be lighter. This is because his body would cast a shadow on the lead leg and the trailing leg would be free of shadows and exposed to the light source.

I think just making the light source more consistent would improve things a lot.

But I like the simplicity of him. His "elasticity" reminds me a bit of Alex Kidd.

Nice start!

I think the first thing that jumps out at me is that from about the knee down the legs don't move during the animation. Imagine trying to lean forward with bending your knees!

You may want to have the character bob straight up and down, rather than leaning forward and back. If you do, then you can have the character's left knee extend out a bit along with their calf. In other words, the feet should be the only non-moving part of the animation (though you could have the feet turn somewhat as well, if you wanted).

I also might recommend slowing down the animation a bit, and maybe pausing a bit at the top and bottom of the animation.

Also, a question: What is the context of the idle? The character looks tense, ready for fighting, perhaps. Is that the case? They seem to have their arms at the ready.

I'll try to work on an edit later today if I get time.