Finally, a truly intimidating balrog not based on the movie's interpretation. I like this a lot. It's not very well defined, but I like how you can sort if make out a feline shaped head by the light of its sword and the glow of its eyes and nostrils while the rest of the demon is shrouded by fire and smoke. Tolkien's description was vague but that made it seem all the more terrifying. Very true to the book.
I really like the way you drawn it, its really awesome how you handled the fire, ash and shadows. it looks epic. however, I dislike the face tho, it reminds me of a kitty, and seems weirdly small in comparison to the body.