Some tiles are missing the outline that most of the tileset keeps as part of the style, especially that wall that I marked, it looks weird because it shares the same color with the floor and it doesn't make sense (Change the floor tiles to other color for an easy fix).
Some characters have a grey shadow, but others have a black one (first screenshot) you might want to fix that too.
Everything else that's marked is just because of the lack of shading/outline for the tiles in that area, just a small detail.