The Thriller is one of Hollywood's most popular forms because it combines the criminality and surprise of the detective form with the danger and pressure of horror.
A good thriller puts the hero in danger early and never lets up. While the thriller usually involves a main character trying to find a murderer, it has very different story beats than the detective genre. Each beat is geared toward wringing every last ounce of terror from the hero and the audience.
Thrillers tend to want to be small. It's like putting your hero in a box and squeezing. One of the advantages of this narrowing of focus is that thrillers maximize emotion. Detective stories, with many more suspects, create a more intellectual experience for the audience. The viewer's main interest is outsmarting the detective, and outsmarting the writer's attempts at sleight of hand. Thrillers let the audience get to know the hero, and the main opponent, with much greater intimacy.
The thriller is also a great strategy if you write independent films. In no other form can you get so much bang for so little money. Casts are small, special effects are nil.
But there is a huge downside to the small size of the thriller form: It puts tremendous pressure on your ability to plot. Whether you write for the Hollywood mainstream or independent film, you have to create a lot of plot in a small space with just a few characters.
It may surprise you to find out that plotting is the least understood area of fiction for screenwriters. We talk all the time about character and dialogue, and just assume that we can come up with a good plot. In fact, plotting requires a very advanced set of techniques that most writers never learn.
Often writers hide their inability to plot behind big action spectacles with lots of characters. But with thrillers you can't hide.
One very good strategy that some writers use is to expand the form itself, to keep the intense pressure but work on a larger canvas. This is a good idea; there are all kinds of techniques for doing that.
But one approach to expanding the thriller I would caution you against -- at least if you want to sell your script to Hollywood -- is writing the political thriller.
A political thriller is a thriller in which the crime and the danger have a national or international source and implications. Examples include 'The 39 Steps,' 'The Manchurian Candidate,' 'Three Days of the Condor' and 'All the President's Men.'
Some very good movies there. But political thrillers are usually much less popular than regular thrillers for five main reasons.
I. The national and international implications are often too complicated to explain and make real to the audience in the film medium -- at least in Hollywood films that emphasize speed over content. (This is one reason political thrillers are much more popular in novels.)
II. Political intrigue is a shadow world that few can identify with.
III. The opposition is a vast system that is almost impossible to focus.
IV. The opposition is so powerful that the hero is reduced to the lowest level; he or she is often no more than a chased rabbit.
V. Political thrillers typically end badly, with the destruction of the individual by the all-powerful system.