I know Smaug from the Michael Hague paintings mostly. In those, his head was REALLY lizard-like, except for the ears, they were like bats' ears. The best I can go for is to suggest something more similar to that.
When JRR made Smaug he usually used a serpentine body, but had a fairly stout neck and large head. The image of smaug on his horde has the longest neck of any of JRR's drawings and it wasn't very long. In his image of smaug been shot over Laketown, Smaug's neck and head are almost like and alliators.
Of course, what JRR wanted is not really that important. Ghost needs to find her Smaug.
You know, the hair and the frills...this looks a lot like your other dragons if you ask me. I like the horns though, kinda a mix between the traditional ones and antlers. His neck appears too thick for the head to me.
Again, you want him to look harsh. This is a creature descended of dark sorceries and the machinations of Morgoth, who was *the* great evil in the world prior to his defeat at the ending of the second age.
So, hard edges, sharp angles. As suggested by others, the mane should go. It's too soft and flowing.
I don't think that more teeth and horns would hurt, though I would reduce or remove his earfrills so they don't take up quite so much space.
In particular, little horns along the line of his jaw and above his eyes would probably help with the fearsome aspect.
The lips need to go or be reduced quite a bit. They look odd and like too heavy makeup.
Hmm. I think if you narrowed his eyes and angled them a bit more, it would help to make him seem more fierce.
Making his muzzle longer and/or more distinct (ie, doesn't flow seamlessly into the rest of his head) might help, but I'm not so sure about that one....
In all honesty, I would first add possible tears/holes in some of the frills as well as reduce the beard. The horn on the nose draws away from the face when the focus should be on the eyes. Then for coloration, try a dull crimson (to suggest age) as well as having bright golden eyes that shine against a dark background. Make the frills a little smaller and I think you have smaug. Hope this helps.