Basically you need a hero/heroine, some sort of plot, a climax and a moral. That's the basis for most recipes as far as screenwriting goes. The problem is some do it better than others.

Sometimes it's painful watching such movies. The moment you realize you can predict every major step along the way, the movie loses part of its charm (unless that's what it intended) and you end up either walking out (though I've personally never done so) or trying to find the good in all the rest: camera work, soundtrack, acting, etc.

There are many, many rules, and following them is something nonconformists in Hollywood adore. Whether it's the token black guy dying (there was a brief period of time when he was allowed to live, maybe even be the hero - see Deep Blue Sea, House On Haunted Hill), or the innocent girl who survives (see most slasher movies) horrors have done it over and over again, yet people still go see them (apparently hope dies last). The bad boy reformed story is as old as time (A Walk To Remember), so is the good boy gone bad, then repenting one (see 21 most recently). And don't get me started on the Chosen One plot. Every martial arts movie out there has something of the sort, so do most comic books (Wanted is the latest one), though I am partial to it, and sometimes, just sometimes we get something different (even if it's a parody - Kung Fu Hustle). I'm not going into teen comedy teritory. Apart from horrors those are the most formulaic of all. Romantic comedies are also right up there, break up to make up plot included. Even the send offs are pretty unoriginal (it's a TV movie, but still - Romantic Comedy 101). Sci-fi is possibly the most original of them (not denying it follows some of the basic themes of adventure, but then again, we're not talking about themes here).

And it doesn't really stop with scripts. Directors are often easily influenced. Roger Ebert, in his review of Battlefield Earth(which uses ) stated the director "has learned from better films that directors sometimes tilt their cameras, but he has not learned why". The unnecessary use of CGI is also quite an issue. Just because someone else does it, it doesn't mean you need it.

You might say it's hard being original, the old "it's all been done before" excuse. But as I've already stated, do it well, and people will overlook cliches, familiar storylines and the likes. Citizen Kane is considered the best movie ever made because it was the first one to use certain camera techniques or tell a certain story. I'm certain Welles wasn't the first to make his camera look up at characters, but he did it with purpose, and it worked. It's because of this (revolutionary) understanding of cinema that his movie still reigns.