I finished The Hobbit for something like the seventh time the day I saw the movie so my perspective is heavily slanted upon that, but frankly, I thought that almost every action scene was overly dramatic. In a sense, it's too much like the crazy action of The Avengers. I'm afraid my suspension of disbelief is lost during the countless parkour scenes and the times they fall dozens of feet without getting hurt. I know dwarves are tough, but sheesh. I'm also not fond of some of the additions. Not because of their very existence, but because of how they were executed. Take Saruman, who I was originally excited to see. He called a white council, not because of the rise of the Necromancer, like in the book, but because of Gandalf's little quest of his own. Saruman disregards the Necromancer in favor of something that should be irrelevant to him. The issue is that although these events are based on events in the book, they play out completely different from how Tolkien would have had them play out, and subjectively it shatters my suspension of disbelief. The reveal of the Fall of Erebor was one of my favorite parts, but I must agree with you on the error of not showing Smaug. You are quite correct, keeping him "hidden" adds nothing. On a first viewing, not seeing him is trivial, but if you consider watching the entire trilogy multiple times, Smaug really should be seen at that part.