This is about genre conceits and "what is cool". AND more importantly, do established Space Opera settings get in the way of your ability to enjoy other settings in the genre? What elements do you like in a Space Opera?... What KILLS Space Opera for you when it raises its head?
Wow, great question. Cool Established Settings:
Babylon 5
Buck Rogers XXV
Dark Matter
Fading Suns
Lightspeed
Pirates of Drinax
Serenity
Star Hero's Terran Empire
Stars Without Numbers (Post-Scream space)
TravellerMap.com
Not Cool Settings (could fill up a page why they are uncool):
Star Trek's Federation
Star Wars
Cool Stuff
A humans-only universe
Ancient technology
Anti-grav tech
Bringing a sword to a blaster fight
Cargo cults
Droids that look like machines
Droids that can pass as human (androids, replicants)
Evil AI's
Genetic engineering (replacement limbs, altered humans)
Humanoid aliens can be cool if done right
Jumpgates
New space religions and cults
Noble houses
NPC aliens that can't be comprehended
Psionics that are not too powerful
Psionics when the focus is on the dramatic elements and not kewl powerz (see Babylon 5)
Ships that spin for gravity
Space combat that's like pirates (broadsides and boarding parties)
Wet nano-tech (inside your body, it can heal you)
Uncool Stuff
AIs that run the PCs ship
Alien PC races that are so alien they are unplayable
Cloning tech (usually)
Dogfights in space
Dry nano-tech (creating/disintegrating objects. See space magic)
Light sabers, etc.
Mecha
Replicators
Space magic (The Force)
Space magic (Treknology)
Space magic (Very powerful psionics)
Teleportation, transporters
The "Better Than You in Every Way" race (Vulcans, Minbari, Space Elves)
The players are plucky rebels fighting an evil empire