I like the texturing and detail, and the faces are cool. However, one thing I've found is if you make an square object slightly tilted, even for a straight on perspective, it looks much more believable. I was working for hours on a computer monitor pixel art, and it just looked flat no matter what I did, until I rotated it just a tad. Maybe this will help your piece.
Also, I know little of shading, but I can not figure out where the light is coming from. If from above, I don't see why it would darken in a circular pattern. If from in front of the door, it seems like the shadow cast on the next highest tier should be horizontal and straight. It looks like the shading on each individual brick is pretty good though, and the shading technique in general.
Keep up the good work.