What is space opera, anyway? Going by the discussion on the preceding blog essay, lots of folks are a bit confused. And so they should be; it's not exactly a well-defined concept.
Dave Langford and Brian Stableford took a stab at describing it in the gigantic monograph on space opera in the Encyclopedia of SF, but they (wisely, in my opinion) didn't try to give it a coherent definition, because it's a diagnosis, not a prescription.
I think that for a work of SF to qualify as space opera it requires certain features to be present. Breadth of scope is one of them: Interstellar scale is almost mandatory (although I think there are exceptions: "Tiger Tiger"/"The Stars my Destination", perhaps). A sense of wonder is necessary as well. The key factor is that it's almost invariably romanticist in sensibility, often overlapping with the gothic: if it lacks a romantic/gothic tone then it's probably not space opera.
I wouldn't call "Ringworld" a space opera, even though it hits the high notes on scale/sense of wonder/adventure—Niven's tone is all wrong—but on the other hand, "The Quantum Thief" trilogy nails the target even though it's not strictly speaking interstellar and a metric shitload of it happens in upload/computing environments. (Jean le Flambeur is a classic space operatic anti-hero in the mold of Gully Foyle.)