In terms of format, I appreciate something like Raymond E. Feist's Riftwar Cycle, where you have a series of connected trilogies. You carry over the universe and some of the characters, but the story is tied up at the end of each trilogy.

Or Fritz Leiber's Fafhrd and the Gray Mouser short stories, which were the individual adventures of those two characters.

There's something obviously appealing about a universe (a "franchise" or "IP", if you must) which goes on and on, but that doesn't mean spending decades on a single story.