Very bland, no real colors D:...
Why are the walls, floor, everything, the same shade of mushy swamp, pale green/gray?
Also, you don't really need to dither on things like the columns, which are flat? If it was intended for shadow, then I guess...? o.o
I messed with it for a few minutes. It felt like coloring a gameboy game XP...
Also, the bricks in the wall shouldnt have so much of the dark outline speckled throughout the bricks, and every little thing doesnt need an outline, use contrast to show edges, different boards, etc.
Didn't really know what to do with your bricks without spending an hour o.o