What do I say about Justice Souter (I'm sure you were on the edge of your seats)? I have little to say about Justice Souter, actually. But since Souter is now departing from the scene I bless you with a little pet theory of mine.
Every once in awhile, through pure accident of history, an individual rises to a position of fame and responsibility in American society for which he has no business rising and for which he or she simply lacked the experience and mental fortitude to cope. In my lifetime, I can think of three such people: Dan Quayle, Janet Reno, and David Souter. There may be others--feel free to nominate your own.
Quayle, Reno, and Souter were all pure accidents of history. Reno, as the third-choice Attorney General because of Bill Clinton's determination to choose a woman. Quayle, well for whatever reason, presumably because Bush wanted a "Jack Kemp-type" but not Jack Kemp, or whatever. And Souter, because as Jan Crawford Greenburg reports, there was no Plan B when Ken Starr got shot down internally.
Having said that, both Quayle and Souter seemed to do a competent job once they got into office. But then again, how would one tell if a VP were incompetent--except, of course, other than creating a public panic over riding the subway. Quayle's was sort of a benign incompetence.
In Souter's case, it is my opinion that Souter's unpreparedness for the job manifested it in his inability to carry the weight of the Supreme Court robe. He never really seemed to have any coherent idea of what the judge's proper role was. Bill Stuntz had a great essay on Powell and O'Connor that I think applies to Souter as well (the link to the original article is broken, but Orin excerpted the key paragraphs here). In that sense, he was similar to Sandra Day O'Connor, a potential "accident of history" contender as well because of Reagan's campaign promise. In my opinion, she too was one of the more mediocre Justice of recent times.
In the end, I don't think that anyone would champion Souter as a anything other than a mediocre Justice. It is hard to measure how "good" a Justice is--one could imagine many different criteria: smarts, influence, coalition-building skills, etc. No matter what criteria one uses, however, doesn't it seem to be the consensus that Souter is certainly near the bottom, if not at the bottom, of the current Court? Perhaps this is an unusually talented Court. But still, Souter is by any measure a weak link on the Court most would think.
Reno, by contrast, was a real menace and her elevation by accident of history was, I think, by most accounts a disaster. Her utter lack of qualifications and temperament for the job left her completely dependent on the Clintons' patronage so she feared above all being fired and returned to obscurity.
What does this say? Not much, I reckon, other than I hope that whoever Obama picks to fill Souter's seat, it will be someone chosen by design and not a panicked elevation by accident of history.
While I have your attention, I'd like to point you to Tom Smith's witty take, "I would like to like Justice Souter". I don't discern any disagreement from Tom about Souter's essential mediocrity.