I don't know, but maybe I was expecting something different, something more....I can't explain it. It just wasn't vivid and memorable enough for me. There's a huge surging build-up of tension that explodes in Moria, the Cave Troll, the Orcs, the crumbling bridges...each more dramatic than the previous so I kind of braced myself for some
real eyecandy, but when the Balrog actually entered I sort of just felt "Is that it?". The only two things that impressed be was when the Balrog roared and when it flashed it's whip around the place, but the creature itself seemed too shadowy and ill-defined at times to be truely memorable.
I came out of the cinema, overjoyed, but when somebody asked me what the Balrog looked like, I couldn't remember.
After seeing it multiple times now, yes, I agree that it is stunning, but yet not jaw dropping.
I was disappointed by the balrog. I think it was the horns or whatever they were. I expected a more man-like and size figure with its menace more implied, I guess.