Love the sprites, you've got a lot of character into those few pixels.
My eyes get a bit freaked out by the transition between the ceilings and the floors. Depending on where I look the ceiling is either one unit higher than the floor or on the same level.
I (very) quickly added the edges you placed next to wall units around the other areas that the ceiling meets the floor. To my eyes this looks a lot more 3D. It's still not quite ideal though, and the points in the previous comment will probably help as well.
What is happening with that chest? Is is embedded in the wall, or is it incredibly narrow, or is it mounted on the wall about a foot from the floor?
I feel like it should be taking up much more of the square tile it's placed on. Just moving it down a lot basically. It could be bigger in that case, too.
Edit: I see what's going on with the chest. I thought the floor behind it was a continuation of the wall from either side of it. That kinda says something about the color hues and values. In that case it is a pixel or so too far down...