Thrillers use suspense to help engage and thrill their audience, generally they also have a cross-genre, and there are many different types.
This type of thriller tends to play with the mind with the audience, where they have to figure out what exactly is going on. This is a very popular type of thriller as they are very suspensful and remain consistent throughout the movie, people also like having a puzzle to solve. There is a big rise in upcoming psychological thrillers because of the recent success of the film 'Inception' which won Bafta, Grammy and Golden Globe awards. This type of thriller has a very large mainstream audience, thus increasing their popularity.
These thrillers involve dangerous love triangles or romance related blackmail. Sometimes they can involve a strong murderous passion. These types of thrillers can be popular as it encourages a woman audience, along with men as there is a thrilling element.
To me these thrillers usually are the scariest by far and they contain quite a lot of false plateaus. We always have the presence of the supernatural force and there is always a fight between the good and evil force.
Policital thrillers are genuinely quite interesting, they sometimes follow historic events in the Government, like the assasination of JFK. These thrillers usually involve corruption of the Government, or those who are against the Government. It can also include spy activity.
These thrillers are very high occtane and usually always involve explosions and fast action of some kind. This type of thriller is also very popular mainly with male audiences. Therefore in 'Salt' changing the gender of the hero is effective in perhaps bringing in female viewers, but still maintaining the conventions of an action thriller film.