Very rarely do I hear people refer to Spielberg as an auteur. If I had to make a guess as to why this was, I would say it was due to the rarity of his name as a writing credit, along with his overall accessibility - publicly & critically. But, that's what makes Spielberg Spielberg.
The true fact of the matter is that Señor Spielbergo may be the truest auteur filmmaker working today - specifically because he rarely writes original material for what he directs. People like Quentin & P.T. firmly establish their respective voices in their respective original screenplays, & their directorial efforts act as a continuation. Of course, their material would look & feel different in someone else's hands, but inaccurately so, which is why they themselves are decent examples of the auteur theory.
The admirable thing about Spielberg is that, not only does he put his specific mark on material written for him (& it is specific) but he embarks on his own unique continuation, & ultimately becomes a writer with the camera; the best illustration of this being Saving Private Ryan. The film's credited screenwriter is Robert Rodat, who also penned the screenplay for the 2000 Roland Emmerich farce, The Patriot. I won't compare the quality of the two films, but I bring it up to suggest the likely triviality of Ryan's physical shooting script. & while Ryan will most likely remain a classic over other films like The Patriot - or Shakespeare In Love for that matter - the first 25 minutes is the clear standout (& to some, standalone) sequence that will act as the primary example as to why it's groundbreaking. The film in its entirety chronicles the first several days of the D-Day invasion - as well as a less compelling, but nevertheless necessary narrative thread - but it's the initial Omaha Beach landing on June 6th that is not only startling in its craft & realism, but structurally so to the rest of the film.
I've seen only the first two Lord of the Rings films, & while I can recall barely anything about them, the one thing that did stick was that the tone of the second film was a sorta building tension to an epic battle - a battle which, ultimately, was head-scratchingly dull. But, regardless of that, that is in essence a basic, familiar story structure. Ryan opens with something that most films can only dream of crescendoing to. Spielberg takes us from the landing craft to the pillbox in what seems like an endless journey, & a movie unto itself. & in this little movie within a movie, we're already cheering on the protagonists whenever they're able to catch a break - & their first big break comes when Dog One is breached in an explosion of sand & smoke.
There are so many films - great films - that unfold & progressively get better with every act. Ryan does that, sure. But so few films can make me excited about just how much movie is left before the credits roll, & evetually leave me wanting more.