That highly detailed shot actually doesn't look that great to me because there is a hard clash between the cartoony main character and the realistic world. The blocky style you're using for this project looks much better IMO.

So here's my two cents: the style you've got looks good. It's unique and pretty. But more color wouldn't hurt it at all. In fact the lack of color is hurting it. Giving each level a different hue would be a step in the right direction, but it would still look somewhat monotonous and boring. You really shouldn't be afraid to use many different colors across a level - your style is already unique enough that adding color variety wouldn't detract from it.

Trust me when I say that color is not your enemy here. IMHO you're actually losing style points for throwing out the color in favor of a more unique style.