The biggest problem is that the sprite don't really appears iso, because the axis seem to be angled to soft. Especially if you imagine the axis of the eyes, the shoulders and the chestline they don't really seem to fit together with the the axes of the hands (the hands are correct in your sprite and a good guideline for looking)
Another proplem is that the upper length of the character seems to be to long for the lower length of the characters. Means you should decrease the length of head and torso and increase the length of the legs.
In my edit I just lengthened the legs, which means that the arms of my edit are currently to short (silly me
).
Palette seems to be just red. I tried to push it more to contrasting colors (yellow-purple) and played a bit around with the saturation - see it as one suggestion. THe color depends anyways on the surrounding graphics.
Your sprite seems to suffer from strong AA to the black outline, You can see this esp. at his front upper arm and the inside of the front leg. Receding this might help the readability.
I am not to fond of the overall black outline, maybe breaking it up here and there with another lighter color might be an idea - it's just a suggestion in my edit.
Another suggestion would be how you solve the shading. Esp. at the head I'd solve it different.
Your sprite currently seems to be very round - to illustrate my point I made my anatomical forms really blocky.