I actually wouldn't go see it in theaters. I haven't seen anything labeled part I and don't plan on it. Why would I knowingly go see a film that isn't going to conclude? What is the climax supposed to be? A fight where the villain wins? Yes, we ALL want that in a superhero movie. If you can't wrap it up in 2-3 hours, then you have failed to tell a quality story.
It's like this Hobbit crap. That book did not warrant 2 movies let alone 3, and I don't plan on seeing any of them mainly for that reason. It's been 20 years since I read them, but I feel like each Lord of the Rings book was longer than the Hobbit, so breaking that into 3 movies means they either suck at story telling or they're adding tons of crap that isn't in the book OR they're simply milking it for more money. For any of those reasons, I have no interest in seeing it and especially paying to see it.
I mean, is there any movie aside from the Empire Strikes Back that ended on a cliffhanger and ended up being a great movie? And of course no one knew that was going to end on a cliffhanger when they went to see it despite it being specifically labeled Part V in the beginning scroll.