Just because his movies get a lot of commercial backing as tentpole type films for the summer... and just because his films hit ridiculously high box office numbers as a result.. does not mean he's the best director out there.
In my opinion, he is entirely over rated. He had an immense budget for Titanic. The studio's backing of the film was beyond anything seen before... the film was out for something like 9 months for god's sakes. At the end of the day, Titanic had a huge, immediate, emotional impact.. but upon multiple viewings.. the story is cheesy, the dialogue can be cringeworthy, the acting is horrible at times, and some of the scenes are nearly unwatchable for me. There's nothing in this movie that makes it worth of it's box office success... ie, better than Gone With the Wind, or Lawrence or Arabia, or similarly epic films.
Avatar is another film that had ridiculous backing - the widest release ever, a huge advertising campaign, and the big draw gimmick of 3D. Watch it without 3D, and it becomes insanely obvious that it's mostly just a boring rip off of Pocohontus - nothing more. The voice over narration feels totally distant, and unneccessary to the main plot. Also, the formulaic narrative at times clashes with film's larger moral narrative. On the one hand, Cameron wants to convay that even though we look different than the "aliens," we're all essentially the same; on the other hand, he asserts that the only real way for the two characters to be with each other is for one of them to forsake their identity and become like the other.
It's all formulaic hollywood hogwash... which is what is marketable... which is what is most enjoyed the common audience.... but it's still crummy storytelling. Give him a small budget, and make him tell a small, personal story without a big spectacle, and then we'll see what he's made of as an artist.
