I agree that the signs need work; the reds lack some readabiltiy, and the shading on the x doesn't make any sense to me. Perhaps if the arrow and x were larger and the signs less detailed?
The ground, water, and clouds all have a good look to them.
Good but as a general rule never tell people what things are in a tileset. If they can't tell for themselves you need to rework something. The only thing I see here that needs work is the reds on the signs; they don't really look like they exist in the same world as the signs do.
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Awesome Tiles!