i think Nolan along with Fincher and I guess Gondry too to a degree, come from the 'style as substance' school and i think if you are an fan of directors with a distinct and well-crafted visual style and their ability to manipulate the context of a scene and also a movie with their style, you would tend to like Nolan and overlook part of his shortcomings as a filmmaker in a traditional sense.
i personally like his movies. i wouldn't go as far as say he's the 'best working director' because i think he hasn't made a movie with a plot that made you fall in love or made you feel the tragedy of the circumstances that the main characters were involved in; aspects to a story that show traditional storytelling skill.
but as far as blockbusters go tho, he might be the best of his era. you might be able to put Spielberg at the same level, but i think Minority Report was his last major blockbuster and that was nearly 10 years ago.
like alot of other posters have said, i think fans of his movies that don't have a deep and extensive knowledge of the history of film would be blown away and rightfully captivated with his movies. i think he's master of the blockbuster, but for him to live up to the name 'best working director', he would have to show more range as a director; like make a movie that was a more traditional character study or with a more traditional plot.
He's kind of like the Nas of directors in that he has a distinctive and highly-skilled style, but he lacks the ability to connect to his audience in emotional terms that the audience naturally relates to.