Even though we didn't see him, his attack in the first film was an amazing scene, such a great sense of power and danger.
Yes, it was terrifying and menacing with its power and mystery.
I've often tried to picture him from his description in the book and sometimes he looks a bit comical to me. But the size they made him the movie makes it seem like it would work better than my first impressions.
I remember as kids, it was very unusual, our mother went to us and said, "I will let you stay up late if you want to watch this movie, you will probably have to read this book someday and it may help you." It was a totally odd suggestion, and we protested that we didn't want to watch some 'literature' movie.
Next day I told her it was a great suggestion and thanked her for it. It was the 70's cartoon of The Hobbit and it's how I usually envisioned Smaug. I think the new movie will show a more menacing and epic Smaug.
Remember, he is powerful enough to destroy the one ring.