Growing up on a farm here in the midwest the archetypal evening meal was some sort of meat (beefsteak, a pork chop, fried chicken, whatever), potatoes (mashed, hashed, french fried, etc.), and a vegetable (usually corns, peas, or carrots). One of the best of these various combos was salisbury steak, mashed potatoes, and peas. The men folk of the family would cut the meat into little cubes and mix both that and the peas into mashed potatoes. It was called the "farm style" of serving such a meal. My mother, having grown up in a sprawling metropolis of some twenty-five hundred souls, wasn't quite used to such displays and occasionally recoiled in horror at such gustatory minglings. (She inherited her own set of weird foods from her Wisconsin-born father, such as "Osh Kosh spaghetti", a soup made from ground beef and the aforementioned noodles.) My palate has broadoned and refined since those bygone days of my youth, but sometimes I still spoon my peas into the mashed potatoes.
My gaming is much the same way. I can get a crapload of fun out of a laser-focused Pendragon or MERP campaign. But I also enjoy running a D&D campaign with copious amounts of deathray robots. I respect guys like Jon, the DM of the World of Alidor, for all the work he's done in creating a weird yet coherent homebrew setting. But I also adore the kind of DM who will whisk his players' paladins and half-orcs off to the wild west milieu of Promise City or the gamma-radiated ruins of Pitzburke. One time my friend Dave and I played Conan and Subotai in his brother-in-law's Greyhawk campaign. It was both totally awesome and an utter travesty. Right now I'm working on a mecha mini-campaign set in the 3rd Imperium, the official campaign world of Traveller. Maybe I ought to go on the Traveller Mailing List and innocently ask for stats for the giant robo-suits of the Imperial Navy. That'd be fun. Mean, but fun.
These sorts of heresies can be a lot of fun, but you need to be careful. Nearly every player I've ever met has had at least one deeply held belief about some setting or another, in much the same way that I don't want to live in a world where Greedo shot first. As silly as such sentiments are, it's important to respect these boundaries. I know some players that wouldn't play Mechas of Imperium 3, simply because the idea of introducing giant robots into that venerable setting would cause great cognitive dissonance. It's important for many players that these mish-mashes not sneak up on them. That's why, despite my transgenre leanings, I am not a fan of bait-and-switch campaign settings. You may have been in one of those yourself in the past. The classic version is a GM who tells you he's running a modern day or sci-fi campaign but at some point the PCs find themselves fighting orcs on Middle Earth. Super-narrow Forgie* designs manage to avoid this sort of situation, but in exchange you miss out the zany fun of whalloping Darth Vader with Mjolnir.
*Is "Forgie" an insult? I hope not, but I'm not sure.
Not your Elves
15 minutes ago