That last bit (spoilers)

Having [spoiler]bruce willis[/spoiler] there really spoiled the ending for me... it's one thing to make an homage to another film, quite another to start putting different characters from one movie into another like what the studios are doing with all of these comic-book franchise movies... seems childish, nerdy and really takes you out of the film experience...

kind of a bait-and-switch move... but that's not the part that really annoys me... it's that it could have clearly been a better movie without that element, if it had to stand on it's own... doing it the way they've done it leaves a bad taste in one's mouth... instead of the movie staying with us while we walk out of the theatre, trying to process the horror, we're immediately thinking about how this story fits into the others and the horror is entirely defused as we play franchise-movie-Tetris...

It's like if you saw Clint Eastwood's Hereafter and then at the end some Wolverine character pops up and sets the movie in the world of X-men and spandex... it'll destroy any spiritual or supernatural elements to it and ruins the mood of the film... It's like having a bite of a McDonalds cheeseburger after having eaten a nice grass-fed steak...

If you watch this movie knowing that it is a part of superhero series it removes a lot of the tension and scariness... Instead of being kidnaped by a deranged young man, you know the girls are kidnaped by some comic-book villain... it's less real, less seems at stake and it's less frightening.

When you watch the movie not knowing about any of the superhero stuff... by the time anything fantastical or supernatural happens you're already on board...

Also, if they didn't need to keep the storyline open for a sequel we could have gotten some climactic kills! Or they could have been freer to take it in another direction.