You can read an excellent roundup of tributes to Andrew Sarris here, and I particularly like this vigorous defense of auteurism by The New Yorker's Richard Brody. (The opposing comments are worth reading too.)
If auteurism were nothing other than the recognition of arcane patterns across a director’s body of work, it would have had a short and obscure run. But in fact, its power comes from its inspiration of artists. Wes Anderson described his primordial auteurist experience when I interviewed him for a Profile that ran in the magazine in 2009. His family’s Betamax tapes of Alfred Hitchcock’s films, “with an orange-colored box for ‘Vertigo’ and a blue one for ‘Rear Window’ and a beige one for ‘The Man Who Knew Too Much,’ ” was a central experience for him as a child:
"Watching those, you know, the name of the director was right there on the front, you were conscious that this guy was a movie artist, it wasn’t an actor and you weren’t reading about how they built the robots or something like that, instead it was some guy whose thing is making images and sounds and things to tell the story."
Auteurism is the mode of criticism through which burgeoning directors identify those established filmmakers in whom they see themselves—and the future of the art form—reflected. It isn’t a matter of seeing patterns but of seeing directors (as if present and holding forth on the other side of the screen) and identifying with them—not by self-abnegation but by elective affinity and imaginative sympathy.