(I only hope this works as I have never used another thumbs before to post a critique. If its ugly, I apologize in advance)

The swirly/curvy architecture looks good but, you may run into a clash if you mix it with the wrong texture sets. In this shot, you have rock walls with an industrial texture set above. IMO it clashes, BUT since I cannot see it all except in this screen, it might work out alright elsewhere.

In this shot, the thing that sticks out is the building in the background. Its not built wrong, its textured... differently. I would try different sets. You might eventually come back to this one but at least try another one. I like the architecture in the front area here. It looks well made. I also like the dim light levels, at least in so far as the screenshot. Sometimes an ingame level is contrary. A few displacements on the ground couldn't hurt. It looks like a tennis court in its flatness.

Run for the hills. There be crabs hereabouts.

Everything in this shot looks superb... Except the ceiling. Its horrible. Trying to make a flat plane look less flat by adding wood is not a good idea. Yeah, it looks OK if you have a castle, but this is not a castle. Try to create some depth by making varying degrees of elevation. Shafts work wonders, as well as a few fans.

Those dips in the wall back yonder, make a few of them deeper, break up the pattern you have going so its less repetitive. I would also think about making the area more diverse in texture choices. Having a wall for instance thats two levels high, with contrasting textures looks better than one 30 foot tall monotonal wall.

This shot looks excellent except... The grounds to flat again. I would also think about how the building is in the rock walls. Usually building show some form of intrusion when built into a wall of rock. Perhaps some cracks or maybe a barrier wall to "hold back" the rocks that are crumbling off. Your building slides in as if its having sex or something.
/2 cents