Playing in Someones Backyard...

Or, RPGs in set worlds
(aka I should be writing novel stuff or amber stuff but I'm not)

Games set in other universes can be fun. Star Wars springs to mind, as does, oh, Marvel or DC comics. The advantages are obvious in saving a GM time (If she knows the setting well enough, if not players can be a pain). The big problem, to me, is canon.
If you set SW in the time of the 4-6 movies (or after, with those heroes running around) and don't play them, you can run into problems. Yeah, sure you can do famous stuff, but they are the big heroes, the gods among men. And if you can't play characters who can equal (or beat) them, then I'd say it's not the Star Wars larger-than-life space opera deal. Comic book universes run into the same problems. What can you do that Superman can't? How can you be a real hero when the Justic League is around and everyone looks up to them?
And, perhaps more importantly, what if they don't react in the right manner to establidshed character? What if they question Leias devotion to the rebellion, or tell Batman to go take a hike because he's just human and, hello, you have superspeed and can kill him before he can react.

One solution is ixnaying the canon setting. To some extent, this will happen. Either during the game or in planning most GMs will diverge from the established setting with some ideas or rules. [The (current(?) (heh)) UA campaign did that to an extent.] I think this works best if the players are allowed to as well, inputing ideas for changes and the like, as long as when all of you look up after the planning is done you're no longer In the Star Trek universe, or whatever. Which might not be bad, but likely what wasn't intended.

Another is to let the players become great heroes, as big as the existning canon ones. The easiest method (short of wiping out the canon big names) is to set the game in an area that doesn't involve them. Earth4, for DC, or a distant part of the federation where no one has ever or will ever or knows anyone who has served on the Enterprise. The players need to be heroes in their own game, not second stringers to the established Canon figures.

The last option I can think of is to throw a massive continuity twist as players. For example, my Amber game is one where Brand *won* the Patternfall War. Other examples....
1) Sauron won the War of the Rings. The PCs are living in the eastlands, protected by the Brown Wizard who didn't want to be involved in the War and is now screwed and angry.
2) Luke turned to the Dark Side, Dad and Son rule the Empire.
3) Big Evil Virus wipes out most mutants. The Big Names are either dead or fled the world or in hiding from the creator of it - humans who know that humanity is going to be extinct soon or something).
4) Do-gooders in Star Trek who think the Prime Directive is immoral and try and help primitives.
5) The Rebellion becomes just as bad as the Empire (it often happens in RL, after alll...)) and the PCs must take down the Canon characters.
6) The communist Federation is under attack from the inside by democracy.
7) Darth Binks. (Okay, that one IS a joke).
8) Go back in history. Set the Canon universe in the Wild West ("Well, Sherrif Kent, you might be a big name in these parts but.."). Or the far future ("The MegaComputer is operational again, and encoded into your brain. We must protect you before the AI of Sauron looks towards you and sends the 9 Nazgul Virii.")

Hmm, about all I can come up with off hand.
Any other thoughts?