I'm not sure how a QT directed Superman film would turn out, but much like alot of QT's directorial efforts, I'm sure it would have been a extremely entertaining film. Both in terms of action, and dialogue. Being a hardcore film buff that he is, I'm sure Quentin would have thrown in some Reeve/Donner Superman references for good measure, and would have also respected those films for both their time and place in the Superman lore, but on the other hand I'm positive QT would have also succeeded in putting his own personal stamp on who, and why Superman is such an American Icon. However, by going "nuts with it", I dont believe he would have attempted to re-write much of the Mythology as previous efforts during the Superman Development Hell saga tried to do, no I believe that he would rather have put in instances into the film that may convey to the audience a different perspective in certain key Superman supporting characters. Which would have definately given the film a much needed edge. Think along the lines of Morrison's All Star supporting cast (which stay true to the characters, but also presents a freshness to them as well) and you get the idea. Also by having the film set in the 1940's (no doubt during WW2 I would imagine), this notion would have presented the film as something truly unique among the Superman movies. Which is a film that retells the story of Superman, during a definate period setting, with much action (possibly more than we have seen in any live action Superman film to date), and no doubt top notch (and extremely quoteable) dialogue.
No director is infallible, but I definately wouldnt have mind a QT directed Superman.