I think the backdrop has too much contrast, and the foreground, not enough.
If anything behind your character is very contrasting it comes across as too busy since your eyes cannot imediately focus onto what the player needs to, characters, enemies and objects. If you are to detail the back I'd make sure it doesn't conflict with the foreground atall.
With your tiles I think you can afford more contrast just so you have better control of shape, by that I dont think just tweaking the contrast higher is really necissery. But just use that black where it can do some good. also the stoney shapes should continue down not just fade off into a shapeless gradient.

quick edit not adressing any colour changes I'd make or anything, just trying to make a small suggestion. Tiling on my behalf could be better.
I did something similar too, but with no real restrictions.
http://pixeljoint.com/pixelart/21234.htmhttp://pixeljoint.com/pixelart/21232.htmIf you're going for a bold coloured style like Kennethfejer tends to do, notice the backdrops are still not as contrasting as the foreground, tending to be slightly dulled down also to draw the focus to where's intended.