You can probably keep this level of detail but tweak the colours to reduce the contrast in the background. In particular, try to avoid those near-black lines between the tiles. It's fine to use for things like solid walls and pits, but it's not very suitable for surfaces players can walk on because of the contrast it has with the lighter parts of the tiles. Just eliminating those black tile borders helps legibility quite a bit, though there's a lot more you can do with reducing the contrast on the floor tiles that may be overlapped by characters.
The characters are very difficult to read against the background, because they all have the same high level of detail and a very similar range of values.
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You can probably keep this level of detail but tweak the colours to reduce the contrast in the background. In particular, try to avoid those near-black lines between the tiles. It's fine to use for things like solid walls and pits, but it's not very suitable for surfaces players can walk on because of the contrast it has with the lighter parts of the tiles. Just eliminating those black tile borders helps legibility quite a bit, though there's a lot more you can do with reducing the contrast on the floor tiles that may be overlapped by characters.