Reflection on Research into Film Openings

From looking into these 5 film openings its become clear that my film opening must establish at least 2 of these factors;

Genre
Setting
Characters

I have found that for my film I would have to establish 2 of these in order to keep the audience incited however mustn't given any too substantial away about the plot. I have noticed that film opening are used to subtly forebode events that may happen later in the film and may aim to do so within mine. On the other hand however 'Spider-man 2' and 'Life of Pi' did not do this, and despite not foreboding what is to come there movie opening where still effective as it would leave vague/subtle hints.
I noticed I have also noticed that the number of actors and actresses may vary due to how many characters with in a story for example 'X-men' would have a bigger cast then 'Juno' as there are more characters with the plot.