Take Jaws for example, the jumping of the shark was ridiculous but you suspend disbelief due to the build up and escalating action through the film,
The Hobbit films unfortunately as well as a lot of movies these days rely on CGI at a detriment to the story and believability of the movie, the original LoTR films had the right amount of CGI and practical effects. The Star Wars prequels had an unholy reliance on CGI and It looks like the new film will have the right amount of each.