I love the exterior shape and intimidating design. My personal recommendation might be to add some external decorations such as wall pillars to break up the flat surfaces and fluff up the walls a bit by throwing in some randomly placed cobblestone, cracked bricks and maybe some brick stairs for the "missing brick" effects and to give it an uneven "rugged" look to it, as if it's stood for a time.
Overall, it looks awesome, especially with the lava moat.