I think the problem is it looking a bit too flat. Never use only black as the outline colour, that never happens in this style. And you need more colours to give it more depth. Most palettes on hats are in at least threes, with up to six or seven altogether with other colours for flash bits or interesting stuff.
EDIT: Just realized that base is quite fat. I'll make a new one tomorrow.
EDIT: Just realized that base is quite fat. I'll make a new one tomorrow.