All-Star Superman has been getting some scholarly attention recently. Here's "Making and Breaking the Superhero Quotidian," by Frank Bramlett. It was published by ImageText, an online journal of interdisciplinary comics studies. It's a pretty good journal. They also published an article on Alan Moore's Superman a while back as part of an entire issue on Moore's work.
Then there's this four-part examination of Morrison's Superman that spans decades' worth of stories. Very thorough, by Jim Dandeneau.