I agree with onek. It's good as it is, but you could take it to a much more satisfying level. =)
Some pointers:
You rely too much on outlines, they get in the way of finer detail; and since there are places where you skipped them, it looks a bit inconsistent. The vertical line down the middle is especially disturbing
The mirroring is too obvious. I see you took the trouble to change the light source on the stone base, but actually the 2 sides would look much more different, either with one in the sun and the other in shadow, or both in the sun but under a considerably different angle.
Actually, just darkening the colors doesn't make it look like shadow, our eye expects different, familiar clues: the roof cast shadows cannot be the same; color shifting is another (outside shadows would be bluer).
This could bring you to a better palette and color conservation: the way you re-used one stone color as a lighter shadow on the other side could be generalized. 44 colors is a lot for a piece like this; think of this not as an abstract goal for its own sake but as a way to unify a piece.
Also, the stone layers should alternate, like this.
More architectural detail like a door, a moat bridge would be nice and help break the symmetry.
There is a wrong perspective in the roof of the little window you added on the left side.
Beware of banding. It's not that easy with isometrics, those pesky 1x2 lines tend to stack up.
The shape is good, but the shading makes it look very flat, I think it'd be better if you added a highlight to each tile/row instead of just every side, I think that'll make it look more solid.
i think if you will take this to the WIP forum u can benefit a lot from that
Thanks. Will be corrected.