Gwaihir said:Usually the campaign evolves into a save the world campiagn and it feels used up after that.
I know a guy who manages to blend both. After each campaign, he tends to advance the timeline a century or a millenia or whatever. The flavor often tends to be different, though there are some constants as well. The flavor can be especially different when the PCs failed to "save the world" in the previous campaign!
Not that that's for everyone, but I thought it was an interesting variation.