if you ask me, the best kind of movie is one where sequels aren't needed, but you still want more.
for example, Lucas coulda ended Star Wars after the first one. the Death Star blows up, Darth Vader flies away, and everyone lives happily ever after... he COULD have ended it, but it's a damn good thing he didn't.
for me, no sequels is worse. if a sequel is bad, it's not like they're going back and changing the original awesome one. Jaws is still a masterpiece, even though the last outing had a roaring, exploding shark fighting Michael Caine in a seaplane