It's a bit...well, plain. You could add a bit more architectural detail (in the form of brushes) where you now have plain or tiled textures, just to make the flat surfaces a bit more varied and 3D. At the very least, split some of those huge flat expanses up with trim textures. Just give the whole map a once-over like that and I'll be happy.
The drop-off into space at the edges is funny, too...I suggest a portal sky with some brushwork buildings to break that effect up.