hmmm...
I found a few things you could improve.
(Thanks, Niek.
)
Maybe you could make the big door a 32x32 pixel sprite instead of a 32x16 one.
So you would have to make the whole tower 16 pixels higher, but the result would look even better. So the perspective of the door wouldn't look that weird.
Furthermore I would make the walkable floor in front of the door 16 pixels wider.
So there would be more space for the tile in front of the upper door.
I would also change the green color of the floor and make it a wooden floor like it was in MM.
And I agree with Niek. You definitely have to make it suitable for a 16x16 pixel grid.
Anyway your sprites are really awesome.
EDIT:
I noticed that the perspective of the upper part of the clock doesn't work.
You have to make the frame of the upper part of the clock wider and the area above smaller.