Doing my daily google for the space opera project, trying to flesh out my reading list (Last read: Heinlein's Space Cadet and Starship Troopers; Current read: Mike Resnick's Starship: Mutiny; next up: Norman Spinrad's The Void-Captain's Tale) I came upon this interesting essay by David Hartwell and Kathryn Cramer, that appeared a couple of years back on SFRevu.

"Many readers and writers and nearly all media fans who entered sf after 1975 have never understood the origin of space opera as a pejorative and some may be surprised to learn of it. Thus the term space opera reentered the serious discourse on contemporary SF in the 1980s with a completely altered meaning: henceforth, space opera meant, and still generally means, colorful, dramatic, large scale science fiction adventure, competently and sometimes beautifully written, usually focussed on a sympathetic, heroic central character, and plot action [this bit is what separates it from other literary postmodernisms] and usually set in the relatively distant future and in space or on other worlds, characteristically optimistic in tone. What is centrally important is that this permits a writer to embark on a science fiction project that is ambitious in both commercial and literary terms."

Worth checking out.