When I go to see a film, I expect to see an entire film, not half of it. To be concluded indeed. They could have at least been a bit inventive with the tagline; when I read those words, I had a sudden urge to travel in time to the Old West to save the Doc.
I want half of my ticket price back.
I'll accept hanging threads and lead-ons. Those are expected, honored storytelling traditions. But I want at least a little closure, not just a big flip-o'-the-bird from the writers.
Sure, the story was fine. All sorts of unresolved, seemingly contradictory bits, but, hey, they have another half a movie in which to resolve them. Woo.