I'm digging the style.
You could experiment with the shading for that room though. I've seen it done as you have it now, and I've seen it done where the darkest shadows are on the back wall, and the lighter shades are on the right and left sides. (Basically, reverse of what there now, if that was too wordy... >.>)
I also think it could benefit from another highlight color or two. (Just on the outside). I think that'd really give it more depth, and roundness, and could even compliment the purple shadowing if you use a yellow hue for the highlights.
On a final note, I think the bricks could use some texture. Nothing too major, but some dithering or something so we know the walls are rough. (As castles tend to be).
I can't wait to see how the floor looks.