What Should An Opening Title Sequence Do?

Opening title sequences are a key element to film as they are the exposition, introducing the genre, action, characters etc. Additionally, it is key that they hook the audience, whether it is visually or aurally, slow paced or beginning fast paced in-media-res, it is important that there is some sort of enigma induced to hook the audience. Opening credits (text) allow the audience to appreciate the people who worked behind the film as, if they are played at the end, most people do not watch them. Also, there is an element of freedom when it comes to the titles with where they are placed and how prominent they are, to ensure that everything is cohesive, if there is a lot of action, usually the credits will be discreet around the action whereas if it is slow paced the titles can appear either large or small anywhere onscreen. 

Here is a video of a, subjective, 10 best opening title sequences. It features different styles of sequences showing how they develop based on different eras and how different styles work better with different genres and storylines.