Review in progress, I'm still reading this one but wanted to pop in and share a quote. Later it'll be stuck at the end with the rest of the quotes.
I'm not a fan of movie cliffhangers - a feeling I can trace back to the second Star Wars movie (Empire Strikes Back - going by film release date, not the series as a whole thing). Because I refer to this example a lot I even have it in my glossary - the Bat-Definitions page - under Han Solo in Carbonite Problem/Rule. Short version: second film cliffhanger resulted in audiences having to wait three years to find out the rest of the story, no internet with spoilers or movie gossip, no book to read, nada as far as sources for plot hints. The result was that I now really dislike cliffhangers in both films and book series (that aren't finished). And it turns out that I'm not the only one that felt like this - because (and now I'm finally getting to the quote!) it's mentioned in this book.
I should also add for those of you who weren't alive or watching movies in the 1980s that film sequels were still a fairly new thing in the 80s (not to be confused with film serials). It wasn't something you could be certain of and there was always the chance that something could happen (a movie could flop, etc.) and the proposed next film might never be made and the story remain unfinished. I think the main reason movie goers now accept the film series/sequels setup is that we've grown used to it, and there's not been an uber-loved cliffhanger-ending-movie that flopped and left viewers with an unresolved story. (Now even movies that don't open to good box office numbers and/or have terrible reviews can still end up making a huge profit in the world market and thus get sequels approved.)
"We put the trailer for Back to the Future Part III (1990) at the end of part two, and the test audience did not like it at all. Unfortunately, there was nothing we could do about it. It had always been our intention to let the audience know that yes, we're leaving you hanging here, but we got the other movie in the can and you're going to see it real soon. We showed that trailer out of a reaction that Bob Zemeckis and I had when we walked out of The Empire Strikes Back; we were pissed off at the fact that Han Solo [Harrison Ford] was left in carbon freeze, that the movie was ending with Darth Vader still at large and that we didn't know if there was going to be another film. So we thought to ourselves that if we're going to leave some threads hanging at the end of Back to the Future II, let's at least tell the audience that's (sic) there's a whole other movie and here's a little taste of it. But they were still upset that the movie ended in a sort of a cliffhanger. I had always argued that part two should have been sold as the second part of the trilogy, so that even before the public went into the theater, they knew that this was part two of three. If we had warned the audience before they saw the movie, they wouldn't have been so upset that the ending left them in the air. Unfortunately, this never happened. Back to the Future II had a record opening, but we fell off 50 percent the next week because audiences thought they were being conned. We should have learned from the test preview; the audience needed to be educated."
Gale is completely right about warning film viewers beforehand - once people know what to expect going in they can be a lot more forgiving. Audiences do not like to be surprised in some aspects of film. Another example aside from cliffhangers, for instance, is letting audiences know what genre the movie is, and advertising it in an honest way. Marketing a movie with various versions of a trailer so that it can seem to be either an action/adventure movie or a romance is often going to annoy/disappoint a chunk of viewers if the movie doesn't quite fit into one or both of those categories.