Stargate SG-1 (Protagonists kill loads of System Lords and change the destiny of the Galaxy) and Blake's 7 (Protagonists struggle against the Terran Federation but get squelched anyway) are both good shows, but for an RPG I don't want to see success or failure totally mandated in the system. Of course it's far harder to 'win' in Paranoia or Call of Cthulu than in Marvel Superheroes or Space Opera (old game). To me D&D comes in-between, genre-wise: it's the perfect system for putting control in the hands of the players with equal chances to succeed or fail by their own efforts. I love DMing generations of PCs in my homebrew world and seeing them shape the world in all sorts of ways. DMing at the highest level for deity PCs like Thrin, almost every session changes the destiny of countries, empires, often the entire world, occasionally the multiverse. I love that. Static, stagnant universes suck.