I think it's down to the individual story. If your story is a massive epic that has to span three books, then by all means leave the endings open. But if the story really is only one book long then I'd feel cheated if it wasn't concluded properly. Like when dodgy horror movies leave some inkling that the antagonist may still be problem, like a loan alien egg survives the vast, film ending explosion. Then they bring out #2 a year later and don't even bother to use the egg that they had set up. Very annoying.
Personally I like huge epic's. Especially if they come in three's (for some reason). So as a potential punter for your work I don't care if it is 95% tied up, or if it's one big cliff hanger. Just don't jeopardize the story by giving it something it doesn't need. i.e a closed ending when really it's open. Or an open ending when really it's closed. I guess the best method (in a multi-book epic) is both. Tie up some sub plots to get that climatic feeling at the end of one book. But leave the main 'Big Bad' hanging. Probably quite hard to do.
I propose that this technique be called The Computer-Game Level Method from hence forth.
Personally I like huge epic's. Especially if they come in three's (for some reason). So as a potential punter for your work I don't care if it is 95% tied up, or if it's one big cliff hanger. Just don't jeopardize the story by giving it something it doesn't need. i.e a closed ending when really it's open. Or an open ending when really it's closed. I guess the best method (in a multi-book epic) is both. Tie up some sub plots to get that climatic feeling at the end of one book. But leave the main 'Big Bad' hanging. Probably quite hard to do.
I propose that this technique be called The Computer-Game Level Method from hence forth.