1) Really boxy, those pillars are the only non-boxy thing I see. Indent some walls, curve some corners, make some cracks in walls, etc.
2) The floor needs to be broken up or the room needs to be smaller, 'cause a huge, flat, perfectly tiled floor could use some more aesthetics in 'er.
3) Add some light fixtures; if you want the map to be dark, then just make them broken light fixtures, but generally speaking a building would still have the wiring/fixtures even if they didn't work.
4) The wall that those pillars are resting on should have a different texture on top, i.e. something that's not bricks.